throttle position BMW 3 SERIES 1988 E30 User Guide

9Unscrew the four bolts, and lift the
carburettor from the insulating flange on the
intake manifold (see illustration).
10If necessary, unscrew the nuts and
remove the insulating flange from the intake
manifold (see illustration).
Refitting
11Refitting is a reversal of removal, but
clean the mating faces thoroughly. The
insulating flange may be re-used, if it’s in
good condition. Adjust the accelerator cable
with reference to Section 9, and the kickdown
cable (where applicable) with reference to
Chapter 7B.
12 Carburettor-
cleaning and adjustment
4
Note:This Section describes the procedure
for the 2B4 carburettor. The procedure for the
2BE carburettor is similar.
Cleaning
1Obtain a complete set of gaskets and seals
for the carburettor.
2Wash clean the exterior surfaces of the
carburettor.3Using a screwdriver, prise the accelerator
pump linkage from the primary throttle arm
(see illustration).
4Unscrew the bolts securing the cover to the
main body. An Allen key is necessary to
remove the centre bolt (see illustration).
5Prise the link from the choke valve plastic
lever (see illustration).
6Lift the cover from the main body, and
remove the gasket (see illustrations).
7Remove the screw securing the throttle
positioner bracket to the throttle housing (see
illustration).
8Disconnect the vacuum unit pullrod from
the secondary throttle lever (see illustration).
Fuel and exhaust systems 4•11
12.3 Using a screwdriver to disconnect
the accelerator pump linkage (arrowed)11.10 Carburettor insulating flange on the
intake manifold can be removed if
necessary11.9 Unscrew the four bolts (arrowed) and
lift the carburettor from the intake
manifold
12.7 Throttle positioner bracket-to-throttle
housing screw (arrowed)12.6c View of the carburettor main body
with the cover removed12.6b View of the underside of the cover
12.6a Lifting the cover from the
carburettor main body12.5 Prise the link (arrowed) from the
choke valve plastic lever12.4 Using an Allen key to remove the
carburettor cover centre bolt
4

12.13e The jet positions in the cover
(arrowed)
4•12 Fuel and exhaust systems
12.13d Secondary bypass air jet (1), TM air
jet (2), and air correction jet (3)12.13c Secondary main jet (left) and TM
fuel jet (right) tightened in the cover
12.13b Secondary main jet (1) and TM
(thermal starter) fuel jet (2)12.13a Unscrew the bypass jet from the
secondary float chamber12.12b . . . then lift out the needle valves,
keeping all components identified side for
side
12.12a Tap out the float pivot pins, and
remove the floats . . .12.11a Throttle housing removed from the
carburettor12.11b Underside of the main body with
throttle housing removed - note gasket
12.10 Primary throttle lever securing nut -
if removed, take care not to disturb the
return spring12.9 Throttle housing-to-main body
securing screws (arrowed)12.8 Disconnecting the vacuum unit
pullrod

9Remove the screws securing the throttle
housing to the main body (see illustration).
10Prise out the intermediate throttle link. If
this proves difficult, unscrew the nut and
disconnect the lever from the primary throttle
spindle, taking care not to disturb the return
spring (see illustration).
11Separate the throttle housing from the
main body, and remove the gasket (see
illustrations).
12With the cover inverted, tap out the float
pivot pins, remove the floats, and lift out the
two needle valves - keeping all the
components identified side for side (see
illustrations).
13Unscrew the bypass fuel jet from the
secondary float chamber, then similarly
remove the jets from the cover - keeping them
all identified for location (see illustrations).
14Clean all the components, and blow all
the internal channels clear using low air
pressure.
15Reassembly is a reversal of dismantling,
but note the following points:
a) Fit the new gaskets and seals supplied in
the repair kit.
b) Before refitting the cover, check that the
choke linkage arm is correctly located in
the lever (see illustration).
c) Check and if necessary adjust the float
settings. Invert the cover, and check thedistance from the contact face (without
gasket) to the top of the float, making sure
that the needle valve spring-tensioned
ball is not depressed (see illustration).
Note that the dimension is different for
the primary and secondary floats (see
Specifications). If adjustment is
necessary, bend the float arm as required.
d) Make sure that the seal is fitted to the top
of the accelerator pump (see
illustration).
Adjustment
Note:Idle speed and mixture adjustments are
covered in Chapter 1.
Automatic choke (2B4)16Check that the automatic choke cover
and housing alignment marks are clearly
visible; if not, make new marks.
17Remove the three screws and withdraw
the metal ring (see illustration).
18Remove the plastic cover, at the same
time disengaging the bi-metal spring from the
control lever (see illustration).
19Fit a rubber band to the bottom of the
control lever. Push the pulldown lever to the
right and use a 4.2 mm diameter drill to check
the distance between the lower edge of the
choke valve and the wall of the carburettor(see illustration). Alternatively apply vacuum
to the pulldown unit to move the lever.
20If adjustment is necessary, turn the screw
on the end of the pulldown unit (see
illustration).
21Refit the cover in reverse order, making
sure that the alignment marks are in line.
Throttle positioner (2B4)
22With the throttle in the idle position, check
that the length of the spring on the throttle
positioner is 23.0 ± 1.0 mm. If not, adjust the
nut as required.
23With no vacuum applied (engine stopped)
check that the control travel, measured
between the stop screw and lever, is 5.0 ±
0.5 mm. If necessary, loosen the locknut and
turn the diaphragm rod as required. Tighten
the locknut on completion.
Fuel and exhaust systems 4•13
12.15b To check the float level, measure
the distance between the contact face and
the top of the float12.15a Choke linkage arm located in the
automatic choke lever
12.20 If adjustment is necessary, turn the
screw (arrowed) on the end of the
pulldown unit
12.19 Fit a rubber band (2) to the bottom
of the control lever, then push the
pulldown lever to the right, and use a
4.2 mm diameter drill (1) to check the
distance between the lower edge of the
choke valve and the wall of the carburettor
12.17 Remove the three screws and
withdraw the metal ring
12.15c Accelerator pump seal (arrowed)
12.18 Remove the automatic choke cover,
at the same time disengaging the bi-metal
spring from the control lever
4

Throttle positioner (2BE)
24Special tools are required to carry out a
comprehensive adjustment on the 2BE
carburettor. This work should therefore be left
to a BMW dealer.
13 Fuel injection -
general information
The fuel injection system is composed of
three basic sub-systems: fuel system, air
intake system and electronic control system.
Fuel system
An electric fuel pump, located inside the
fuel tank or beside the fuel tank, supplies fuel
under constant pressure to the fuel rail, which
distributes fuel evenly to all injectors. From
the fuel rail, fuel is injected into the intake
ports, just above the intake valves, by the fuel
injectors. The amount of fuel supplied by the
injectors is precisely controlled by an
Electronic Control Unit (ECU). An additional
injector, known as the cold start injector (L-
Jetronic and early Motronic systems only),
supplies extra fuel into the intake manifold for
starting. A pressure regulator controls system
pressure in relation to intake manifold
vacuum. A fuel filter between the fuel pump
and the fuel rail filters the fuel, to protect the
components of the system.
Air intake system
The air intake system consists of an air filter
housing, an airflow meter, a throttle body, the
intake manifold, and the associated ducting.
The airflow meter is an information-gathering
device for the ECU. These models are
equipped with the vane-type airflow meter. A
potentiometer measures intake airflow, and a
temperature sensor measures intake air
temperature. This information helps the ECU
determine the amount of fuel to be injected by
the injectors (injection duration). The throttle
plate inside the throttle body is controlled by
the driver. As the throttle plate opens, the
amount of air that can pass through the
system increases, so the potentiometer opens
further and the ECU signals the injectors to
increase the amount of fuel delivered to the
intake ports.
Electronic control system
The computer control system controls the
fuel system and other systems by means of
an Electronic Control Unit (ECU). The ECU
receives signals from a number of information
sensors which monitor such variables as
intake air volume, intake air temperature,
coolant temperature, engine rpm,
acceleration/deceleration, and exhaust
oxygen content. These signals help the ECU
determine the injection duration necessary for
the optimum air/fuel ratio. These sensors and
their corresponding ECU-controlled outputactuators are located throughout the engine
compartment. For further information
regarding the ECU and its relationship to the
engine electrical systems and ignition system,
refer to Chapters 5 and 6.
Either an L-Jetronic system or a Motronic
system is fitted. Later models have an
updated version of the original Motronic
system.
14 Fuel injection systems
L-Jetronic fuel injection system
The Bosch L-Jetronic fuel injection system
is used on most 3-Series models up to 1987,
and on most E28 (“old-shape”) 5-Series
models. It is an electronically-controlled fuel
injection system that utilises one solenoid-
operated fuel injector per cylinder. The system
is governed by an Electronic Control Unit
(ECU) which processes information sent by
various sensors, and in turn precisely
meters the fuel to the cylinders by
adjusting the amount of time that the injectors
are open.
An electric fuel pump delivers fuel under
high pressure to the injectors, through the fuel
feed line and an in-line filter. A pressure
regulator keeps fuel available at an optimum
pressure, allowing pressure to rise or fall
depending on engine speed and load. Any
excess fuel is returned to the fuel tank by a
separate line.
A sensor in the air intake duct constantly
measures the mass of the incoming air, and
the ECU adjusts the fuel mixture to provide an
optimum air/fuel ratio.
Other components incorporated in the
system are the throttle valve (which controls
airflow to the engine), the coolant temperature
sensor, the throttle position switch, idle
stabiliser valve (which bypasses air around
the throttle plate to control idle speed) and
associated relays and fuses.
Motronic fuel injection system
The Motronic system combines the fuel
control of the L-Jetronic fuel injection system
with the control of ignition timing, idle speed
and emissions into one control unit.
The fuel injection and idle speed control
functions are similar to those used on the L-
Jetronic system described above. For more
information on the Motronic system, see
Chapter 6.
An oxygen sensor is mounted in the
exhaust system on later models with a
catalytic converter. This sensor continually
reads the oxygen content of the exhaust gas.
The information is used by the ECU to adjust
the duration of injection, making it possible to
adjust the fuel mixture for optimum converter
efficiency and minimum emissions.
15 Fuel injection system-
check
2
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Don’t work in a
garage where a natural gas-type appliance
(such as a water heater or clothes dryer)
with a pilot light is present. If you spill any
fuel on your skin, rinse it off immediately
with soap and water. When you perform
any kind of work on the fuel system, wear
safety glasses, and have a fire
extinguisher on hand.
1Check the earth wire connections. Check
all wiring harness connectors that are related
to the system. Loose connectors and poor
earths can cause many problems that
resemble more serious malfunctions.
2Make sure the battery is fully charged, as
the control unit and sensors depend on an
accurate supply voltage in order to properly
meter the fuel.
3Check the air filter element - a dirty or
partially-blocked filter will severely impede
performance and economy (see Chapter 1).
4If a blown fuse is found, renew it and see if
it blows again. If it does, search for an earthed
wire in the harness related to the system.
5Check the air intake duct from the airflow
meter to the intake manifold for leaks. Intake
air leaks can cause a variety of problems. Also
check the condition of the vacuum hoses
connected to the intake manifold.
6Remove the air intake duct from the throttle
body, and check for dirt, carbon and other
residue build-up. If it’s dirty, clean it with
carburettor cleaner and a toothbrush.
7With the engine running, place a
screwdriver or a stethoscope against each
injector, one at a time, and listen for a clicking
sound, indicating operation (see illustration).
4•14 Fuel and exhaust systems
15.7 Use a stethoscope or screwdriver to
determine if the injectors are working
properly - they should make a steady
clicking sound that rises and falls with
engine speed changes

8Check the fuel system pressure (see
Section 3).
9If these checks do not locate the problem,
take the vehicle to a BMW dealer, who will be
able to read the fault codes stored in the ECU,
using special equipment.
16 Airflow meter- check,
removal and refitting
2
Check (L-Jetronic systems)
1Remove the duct from the intake end of the
airflow meter. Carefully open and close the
sensor flap (see illustration), and check for
binding. The flap can bend during a backfire,
and cause incorrect resistance readings. The
flap will bind and stick in a partially-open
position, causing the engine to run rich, and
stall when it returns to idle.
2Disconnect the electrical connector from
the airflow meter.
3Using an ohmmeter, check the resistancebetween terminals 7 and 8 (see illustration).
The resistance should increase steadily
(without any “flat spots”) as the sensor flap is
slowly moved from the fully-closed position to
the fully-open position.
4Also, check the intake air temperature
sensor (inside the airflow meter). Using an
ohmmeter, probe terminals 8 and 9 (see
illustration 16.3)and check for the proper
resistance. The resistance should be 2200 to
2700 ohms at 20º C.
5If the resistance readings are correct, check
the wiring harness (see Chapter 12). Plug in
the connector to the airflow meter. Ensure
that the ignition is switched off. Disconnect
the electrical connector from the ECU (located
under the right-hand side of the facia) and
probe terminals 7 and 8 (see illustration)with
an ohmmeter. Carefully move the door of the
airflow meter, and observe the change in
resistance as it moves from closed to fully-
open. The test results should be the same as
paragraph 3. If there are any differences in the
test results, there may be a shorted-out or
broken wire in the harness.
Check (Motronic systems)
6Ensure that the ignition is switched off.Remove the ECU access cover (see Chap-
ter 6) and disconnect the harness connector
(see illustration).
7Using an ohmmeter, probe the designated
terminals of the ECU electrical connector (see
illustrations)and check for the proper
change in resistance while moving the sensor
flap. On early Motronic systems, probe
terminals 7 and 9. On later Motronic systems,
probe terminals 7 and 12. The resistance
should increase steadily (without any “flat
spots”) as the sensor flap is slowly moved
from the fully-closed position to the fully-open
position. Note: Early Motronic systems are
distinguishable by the 35-pin ECU electrical
connector; later Motronic systems use a 55-
pin connector.
8If the resistance readings are incorrect,
check the wiring harness.
Removal and refitting (all
systems)
9Disconnect the electrical connector from
the airflow meter.
10Remove the air cleaner assembly (see
Section 8).
11Remove the nuts (see illustrations), and
lift the airflow meter from the engine
compartment or from the air cleaner
assembly.
12Refitting is the reverse of removal.
Fuel and exhaust systems 4•15
16.5 The ECU is located under the right-
hand side of the facia. Unplug the
electrical connector, and check the
resistance between terminals 7 and 8 as in
paragraph 3. The test results should be the
same.
16.3 Connect an ohmmeter to terminals 7
and 8 of the airflow meter, and check for a
smooth change in resistance as the vane
door of the airflow meter is slowly opened
and closed16.1 Check for binding of the flap in the
airflow meter as it nears closing position
or wide-open position. Any hesitation or
binding will cause erratic idle conditions,
rich fuel mixture or poor acceleration and
throttle response (airflow meter removed
for clarity)
16.7b Unplug the connector, connect the
ohmmeter probes to terminals 7 and 9
(early Motronic systems) and check for a
smooth change in resistance as the door
on the airflow meter is slowly opened and
closed16.7a Connect the ohmmeter probes to
terminals 7 and 12 (later Motronic systems)
of the ECU connector and check for a
smooth change in resistance as the door
on the airflow meter is slowly opened and
closed16.6 Remove the under-facia panel to gain
access to the ECU on Motronic systems
(left-hand-drive model shown)
4

17 Throttle body- check,
removal and refitting
2
Check
1Detach the air intake duct from the throttle
body (see Section 8) and move the duct out of
the way.
2Have an assistant depress the throttle
pedal while you watch the throttle valve.
Check that the throttle valve moves smoothly
when the throttle is moved from closed (idle
position) to fully-open (wide-open throttle).
3If the throttle valve is not working properly,
renew the throttle body unit.
Warning: Wait until the engine is
completely cool before beginning
this procedure.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
Removal and refitting
4Detach the battery negative cable.
5Detach the air intake duct from the throttle
body, and place to one side.
6Detach the accelerator cable from the
throttle body (see Section 9).
7Detach the cruise control cable, if applicable.
8Clearly label all electrical connectors
(throttle position sensor, cold start injector,
idle air stabiliser, etc), then unplug them.
9Clearly label all vacuum hoses, then detach
them.
10Unscrew the radiator or expansion tank
cap to relieve any residual pressure in the
cooling system, then refit it. Clamp shut the
coolant hoses, then loosen the hose clamps
and detach the hoses. Be prepared for some
coolant leakage.11Remove the throttle body mounting nuts
(upper) and bolts (lower), and detach the
throttle body from the air intake plenum (see
illustration).
12Cover the air intake plenum opening with
a clean cloth, to prevent dust or dirt from
entering while the throttle body is removed.
13Refitting is the reverse of removal. Be sure
to tighten the throttle body mounting nuts to
the torque listed in this Chapter’s Specifica-
tions, and adjust the throttle cable (see
Section 9) on completion.
18 Fuel pressure regulator-
check and renewal
3
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Don’t work in a
garage where a natural gas-type appliance
(such as a water heater or clothes dryer)
with a pilot light is present. If you spill any
fuel on your skin, rinse it off immediately
with soap and water. When you perform
any kind of work on the fuel system, wear
safety glasses, and have a fire
extinguisher on hand.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
Check
1Depressurise the fuel system (see Sec-
tion 2).
2Detach the battery negative cable.
3Disconnect the fuel line and connect a fuel
pressure gauge (see Section 3). Reconnect
the battery.4Pressurise the fuel system (refit the fuel
pump fuse and switch on the ignition), and
check for leakage around the gauge
connections.
5Connect a vacuum pump to the fuel
pressure regulator (see illustration).
6Run the fuel pump (see Section 3). Read the
fuel pressure gauge with vacuum applied to
the pressure regulator, and also with no
vacuum applied. The fuel pressure should
decrease as vacuum increases.
7Stop the fuel pump and reconnect the
vacuum hose to the regulator. Start the engine
and check the fuel system pressure at idle,
comparing your reading with the value listed
in this Chapter’s Specifications. Disconnect
the vacuum hose and watch the gauge - the
pressure should jump up to maximum as soon
as the hose is disconnected.
8If the fuel pressure is low, pinch the fuel
return line shut and watch the gauge. If the
pressure doesn’t rise, the fuel pump is
defective, or there is a restriction in the fuel
feed line. If the pressure now rises sharply,
renew the pressure regulator.
9If the indicated fuel pressure is too high,
stop the engine, disconnect the fuel return line
and blow through it to check for a blockage. If
there is no blockage, renew the fuel pressure
regulator.
10If the pressure doesn’t fluctuate as
described in paragraph 7, connect a vacuum
4•16 Fuel and exhaust systems
18.5 Carefully watch the fuel pressure
gauge as vacuum is applied (fuel pressure
should decrease as vacuum increases)
17.11 Remove the nuts (arrowed) and lift
the throttle body from the intake manifold
(the two lower bolts are hidden from view)16.11b Remove the nuts (arrowed) from
the air cleaner housing, and detach the
airflow meter16.11a Push the tab and remove the air
duct from inside the air cleaner assembly

2L-Jetronic systems are equipped with a
separate idle speed control unit (computer)
located under the facia. The idle air stabiliser
valve has an adjusting screw. Early models
are equipped with plastic valves, but they still
can be adjusted by removing the hose and
inserting a very thin screwdriver inside.
3Early Motronic systems are also equipped
with a separate idle speed control unit
(computer) located under the facia. The idle
air stabiliser valve has an adjusting screw.
4On later Motronic systems, the idle air
stabiliser valve is ECU-controlled, and no
provision is made for adjustment.
Preliminary check
5Before performing any checks on the idle
air stabiliser valve, make sure these criteria
are met:
a) The engine must be at operating
temperature (60ºC)
b) Turn off all electrical accessories (air
conditioning, heater controls, headlights,
auxiliary cooling fan, etc)
c) The throttle position sensor must be
operating correctly (see Chapter 6)
d) There must not be any exhaust leaks
e) There must not be any vacuum leaks
f) Where fitted, the oxygen sensor must be
operating properly (see Chapter 6)
6Connect a tachometer in accordance with
the manufacturer’s instructions.
Caution: The ignition must be
switched off before making any
electrical connections.
7The idle air stabiliser valve operates
continuously when the ignition is on. Start the
engine and make sure the valve is vibrating
and humming slightly.
L-Jetronic system
Check
8With the engine running, disconnect the
electrical connector from the valve. The idle
speed should increase to about 2,000 rpm.
9If the idle speed does not increase, turn the
engine off. Using an ohmmeter, check the
resistance across the terminals of the valve(see illustration). It should be 9 to 10 ohms
with the ambient air temperature at about
20º C.
10Using a pair of jumper wires, apply battery
voltage to the valve, and confirm that the
valve closes tightly. When the voltage is
removed, the valve should re-open.
11If the idle air stabiliser valve fails any of
the tests, renew it.
12If the idle air stabiliser valve passes the
tests, check the control current.
13Unplug the electrical connector from the
valve. Using a jumper wire, connect one
terminal of the electrical connector to one of
the terminals on the valve, Connect an
ammeter (0 to 1000 mA range) between the
other terminal on the electrical connector and
the remaining terminal on the valve. Start the
engine and allow it to idle. With the engine
running, the current reading should be
between 400 and 500 mA. Adjust the valve if
the current reading is not as specified (see
paragraph 15). Note: The idle air stabiliser
current will fluctuate between 400 and
1100 mA if the engine is too cold, if the
coolant temperature sensor is faulty, if the idle
speed needs to be adjusted, if there is an
engine vacuum leak or if electrical accessories
are on.
14If there is no current reading, have the idle
speed control unit diagnosed by a BMW
dealer or other specialist. Note: The idle air
stabiliser control unit (located under the facia)
can develop an electrical connector problem
that intermittently turns the valve on and off.
Check the connector very carefully before
fitting any new parts. Sometimes, a new
control unit will only fix the problem
temporarily.
Adjustment
15With the ignition switched off, connect a
tachometer in accordance with the equipment
manufacturer’s instructions.
16Make sure the ignition timing is correct
(see Chapter 5).
17Connect an ammeter to the valve (see
paragraph 13).
18With the engine running, the current
reading should be 450 to 470 mA at 850 to900 rpm (manual transmission), or 460 to
480 mA at 850 to 900 rpm (automatic
transmission).
19If the control current is not correct, turn
the adjusting screw until it is within the correct
range (see illustration). Note: On metal-type
valves, the adjusting screw is mounted
externally. On plastic-type valves, the
adjustment screw is inside, and can be
reached by removing the hose at the end of
the valve.
Motronic systems
Check
Note:There are two types of idle air stabiliser
valve on these systems; early models usually
have a two-wire valve, while later models are
equipped with a three-wire valve.
20With the engine running, disconnect the
electrical connector from the valve. The idle
speed should increase to about 2000 rpm.
21If the idle speed does not increase:
a) Two-wire valve - Using a pair of jumper
wires, apply battery voltage to the valve,
and confirm that the valve closes tightly.
When the voltage is removed, the valve
should re-open. Also, check the
resistance of the valve (see illus-
tration 21.9). The resistance should be
about 9 or 10 ohms.
b) Three-wire valve - Turn the engine off and
unplug the electrical connector from the
valve. Using an ohmmeter, check the
resistance on the two outer terminals of
the valve. (see illustration). It should be
about 40 ohms. Check the resistance on
the centre and outside terminals of the
valve. They should both be about
20 ohms.
22If the idle air stabiliser valve fails any of
the tests, renew it.
23If the idle air stabiliser valve tests are all
correct, check the control current (two-wire
valve) or the voltage (three-wire valve) as
follows.
24On two-wire valves, connect an ammeter
(0 to 1000 mA range) as described in
paragraph 13. Start the engine, and allow it to
idle. With the engine running, the current
Fuel and exhaust systems 4•19
21.21 Check the idle air stabiliser valve
resistance on the two outer terminals on
later Motronic systems - it should be about
40 ohms21.19 Location of the adjustment screw on
the metal-type idle air stabiliser valve
(L-Jetronic system)21.9 Check the resistance of the idle air
stabiliser valve - it should typically be 9 to
10 ohms (L-Jetronic system)
4

Fuel injection system - fault finding
L-Jetronic fuel injection system
Engine difficult to start, or fails to start (when cold)
Probable cause Corrective action
Cold start injector or thermotime switch faulty Test cold start injector and thermotime switch. Renew faulty components (see Section 19)
Fuel pump inoperative Check fuel pump fuse and fuel pump relay (see Sections 3 and 4)
Airflow meter flap (door) binding or stuck
in open position Inspect the airflow meter for damage (see Section 16)
Fuel pressure incorrect Test system pressure (see Section 3). Test fuel pressure regulator (Section 18)
Intake air leaks Inspect all vacuum lines, air ducts, and oil filler and dipstick seals
Fuel injectors clogged or not operating Check fuel injectors (see Section 20) and wiring harness
Coolant temperature sensor faulty or
wiring problem Test coolant temperature sensor (see Chapter 6, Section 4)
Throttle position sensor (TPS) incorrectly adjusted Check TPS adjustment (see Chapter 6, Section 4)
Incorrect ignition timing Check ignition timing (see Chapter 5). Check vacuum advance system
Dirt or other contaminants in fuel Check the fuel and drain the tank if necessary
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Engine difficult to start, or fails to start (when warm)
Probable cause Corrective action
Cold start injector leaking or operating continuously Test cold start injector and thermotime switch (see Section 19)
Fuel pressure incorrect Test fuel pump(s). Renew if necessary (see Section 3)
Insufficient residual fuel pressure Test residual fuel pressure. Renew fuel pump or fuel accumulator as necessary
(see Section 18)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks. Correct leaks as required (see Chapter 4)
Coolant temperature sensor faulty or
wiring problem Test coolant temperature sensor (see Chapter 6, Section 4)
Vapour lock (warm weather) Check fuel pressure (see Section 3)
EVAP system faulty (where applicable) Check EVAP system (see Chapter 6, Section 6)
Incorrect ignition timing Check ignition timing (see Chapter 5). Check vacuum advance system
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Idle speed control system faulty Test the idle air stabiliser valve (see Section 21)
Engine misses and hesitates under load
Probable cause Corrective action
Fuel injector clogged or faulty Test fuel injectors. Check for clogged injector lines. Renew faulty injectors (see Section 20)
Fuel pressure incorrect Test fuel system pressure (see Section 3). Test fuel pressure regulator (see Section 18)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks (see Chapter 4)
Engine maintenance Tune-up engine (see Chapter 1). Check the distributor cap, rotor, HT leads and spark
plugs, and renew any faulty components
Airflow meter flap (door) binding, or
stuck in open position Inspect the airflow meter for damage (see Section 16)
Intake air leaks Inspect all vacuum lines, air ducts and oil filler and dipstick seals
Engine has erratic idle speed
Probable cause Corrective action
Idle air stabiliser valve faulty Check the idle air stabiliser valve (see Section 21)
No power to the idle air stabiliser valve Check the idle air stabiliser relay and wiring circuit (see Chapter 12)
Vacuum advance system faulty Check vacuum advance system and electronic vacuum advance relay
Idle speed control unit faulty Have the idle speed control unit checked by a dealer
Motronic fuel injection system
Note:With this system, when faults occur, the ECU stores a fault code in its memory. These codes can only be read by a BMW dealer, as
specialised equipment is required. It may save time to have at least the initial fault diagnosis carried out by a dealer.
Lack of power
Probable cause Corrective action
Coolant temperature sensor faulty, Test coolant temperature sensor and wiring. Repair wiring or renew sensor if
or wire to sensor broken faulty (see Chapter 6)
Fuel pressure incorrect Check fuel pressure from main pump and transfer pump, as applicable (see Section 3)
Throttle plate not opening fully Check accelerator cable adjustment to make sure throttle is opening fully. Adjust cable if
necessary (see Section 9)
Fuel and exhaust systems 4•21
4

Engine difficult to start, or fails to start (when cold)
Probable cause Corrective action
Cold start injector or thermotime switch
faulty (early Motronic system only) Test cold start injector and thermotime switch. Renew faulty components (see Section 19)
Fuel pump not running Check fuel pump fuse and fuel pump relay (see Sections 2 and 3)
Airflow meter flap (door) binding, or
stuck in open position Inspect the airflow meter for damage (see Section 16)
Fuel pressure incorrect Test system pressure (see Section 3)
Intake air leaks Inspect all vacuum lines, air ducts and oil filler and dipstick seals
Fuel injectors clogged or not operating Check fuel injectors (see Section 20) and wiring harness
Coolant temperature sensor faulty or Test coolant temperature sensor (see Chapter 6, Section 4)
wiring problem
TPS (throttle position sensor) incorrectly adjusted Check TPS adjustment (see Chapter 6, Section 4)
Dirt or other contaminants in fuel Check the fuel and drain the tank if necessary
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Crankshaft position signal missing Faulty position sensor or flywheel, or reference pin missing (see Chapter 5)
Engine difficult to start, or fails to start (when warm)
Probable cause Corrective action
Cold start injector leaking or operating
continuously (early Motronic system only) Test cold start injector and thermotime switch (see Section 19)
Fuel pressure incorrect Test fuel pressure (see Section 3)
Insufficient residual fuel pressure Test fuel system hold pressure (see Section 3)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks. Correct leaks as necessary
Coolant temperature sensor faulty
or wiring problem Test coolant temperature sensor (see Chapter 6, Section 4)
Vapour lock (in warm weather) Check fuel pressure (see Section 3)
EVAP system faulty Check EVAP system (see Chapter 6, Section 6)
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Idle speed control system faulty Test the idle air stabiliser valve (see Section 21)
Oxygen sensor faulty (where applicable) Check the oxygen sensor (see Chapter 6, Section 4)
Engine misses and hesitates under load
Probable cause Corrective action
Fuel injector clogged Test fuel injectors. Check for clogged injector lines. Renew faulty injectors (see Section 20)
Fuel pressure incorrect Test fuel system pressure (see Section 3). Test fuel pressure regulator (see Section 18)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks (see Chapter 4)
Engine maintenance Tune-up engine (see Chapter 1). Check the distributor cap, rotor, HT leads and spark
plugs, and renew any faulty components
Airflow meter flap (door) binding, or Inspect the airflow meter for damage (see Section 16)
stuck in open position
Intake air leaks Inspect all vacuum lines, air ducts, and oil filler and dipstick seals
Throttle position sensor (TPS) incorrectly adjusted Check TPS adjustment (see Chapter 6)
Engine idles too fast
Probable cause Corrective action
Accelerator pedal, cable or throttle valve binding Check for worn or broken components, kinked cable, or other damage. Renew faulty
components
Air leaking past throttle valve Inspect throttle valve, and adjust or renew as required
Engine has erratic idle speed
Probable cause Corrective action
Idle air stabiliser valve faulty Check the idle air stabiliser valve (see Section 21)
No power to the idle air stabiliser valve Check the idle air stabiliser relay and wiring circuit (see Chapter 12)
Idle speed control unit faulty Have the idle speed control unit checked by a dealer
Poor fuel economy
Probable cause Corrective action
Cold start injector leaking
(early Motronic system only) Test and, if necessary, renew cold start injector (see Section 19)
Oxygen sensor faulty (where applicable) Test the oxygen sensor (see Chapter 6, Section 4))
Sticking handbrake/binding brakes Check the handbrake/braking system (see Chapter 9)
Tyre pressures low Check tyre pressures (Chapter 1)
4•22 Fuel and exhaust systems

Check
12Warm up the engine, and let it run at idle.
Disconnect the oxygen sensor electrical
connector, and connect the positive probe of
a voltmeter to the oxygen sensor output
connector terminal (refer to the following
table) and the negative probe to earth (see
illustrations).
Note:Most oxygen sensor electrical
connectors are located at the rear of the
engine, near the bulkhead. Look for a large
rubber boot attached to a thick wire harness.
On early 535i models, the connector for the
oxygen sensor heater circuit is under the
vehicle. Look for a small protective cover.
These models should have the updated
oxygen sensor fitted, to make access similar
to other models. Consult your dealer service
department for additional information.
13Increase and then decrease the engine
speed, and monitor the voltage.
14When the speed is increased, the voltage
should increase to 0.5 to 1.0 volts. When the
speed is decreased, the voltage should fall to
about 0 to 0.4 volts.
15Also where applicable, inspect the oxygen
sensor heater (models with multi-wire
sensors). With the ignition on, disconnect the
oxygen sensor electrical connector, and
connect a voltmeter across the terminals
designated in the chart (see below). There
should be battery voltage (approximately
12 volts).
16If the reading is not correct, check the
oxygen sensor heater relay (see Chapter 12).
If the information is not available, check the
owner’s handbook for the exact location of
the oxygen sensor heater relay. The relay
should receive battery voltage.
17If the oxygen sensor fails any of these
tests, renew it.
Renewal
Note: Because it is fitted in the exhaust
manifold, converter or pipe, which contracts
when cool, the oxygen sensor may be very
difficult to loosen when the engine is cold.
Rather than risk damage to the sensor(assuming you are planning to re-use it in
another manifold or pipe), start and run the
engine for a minute or two, then switch it off.
Be careful not to burn yourself during the
following procedure.
18Disconnect the battery negative cable.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
19Raise and support the vehicle.
20Disconnect the electrical connector from
the sensor.
21Carefully unscrew the sensor.
Caution: Excessive force may
damage the threads.
22A high-temperature anti-seize compound
must be used on the threads of the sensor, to
facilitate future removal. The threads of new
sensors will already be coated with this
compound, but if an old sensor is removed
and refitted, recoat the threads.23Refit the sensor and tighten it securely.
24Reconnect the electrical connector of the
pigtail lead to the main engine wiring harness.
25Lower the vehicle, and reconnect the
battery.
Oxygen Sensor Heated power
sensor type output signal supply (12V)
Unheated
(single-wire) black wire (+) Not applicable
Heated terminal 1 (+) terminals
(three-wire) 3 (+) and 2 (-)
Heated terminal 2 (+) terminals
(four-wire) 4 (+) and 3 (-)
Throttle Position Sensor (TPS)
General description
26The Throttle Position Sensor (TPS) is
located on the end of the throttle shaft on the
throttle body. By monitoring the output
voltage from the TPS, the ECU can determine
fuel delivery based on throttle valve angle
(driver demand). In this system, the TPS acts
as a switch rather than a potentiometer. One
set of throttle valve switch contacts is closed
(continuity) only at idle. A second set of
contacts closes as the engine approaches
full-throttle. Both sets of contacts are open
(no continuity) between these positions. A
broken or loose TPS can cause intermittent
bursts of fuel from the injector and an
unstable idle, because the ECU thinks the
throttle is moving.
27All models (except for early 535i models
with automatic transmission) combine the idle
and full-throttle switch; a separate idle
position switch indicates the closed-throttle
position, while the TPS is used for the full-
throttle position. On 535i models with
automatic transmission, the TPS is connected
directly to the automatic transmission control
unit. With the throttle fully open, the
transmission control unit sends the full-
throttle signal to the Motronic control unit.
All models except early 535i with
automatic transmission
Check
28Remove the electrical connector from the
TPS, and connect an ohmmeter to terminals 2
and 18 (see illustrations). Open the throttle
Engine management and emission control systems 6•3
4.12b These oxygen sensor terminal
designations are for the harness side only.
Use the corresponding terminals on the
sensor side for the testing procedures
(there are three different four-wire oxygen
sensor connectors available - don’t get
them mixed up)4.12a The oxygen sensor, once it is
warmed up (320º C), puts out a very small
voltage signal. To verify it is working,
check for voltage with a digital voltmeter
(the voltage signals usually range from
0.1 to 1.0 volt)
4.28b First check for continuity between
terminals 2 and 18 with the throttle closed
(later Motronic system shown) . . .4.28a The TPS on L-Jetronic systems is
located under the intake manifold
(terminals arrowed)
6