change key battery OPEL FRONTERA 1998 Workshop Manual
[x] Cancel search | Manufacturer: OPEL, Model Year: 1998, Model line: FRONTERA, Model: OPEL FRONTERA 1998Pages: 6000, PDF Size: 97 MB
Page 1232 of 6000

6E–115 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0108 MAP Sensor Circuit High Voltage
D06RW102
Circuit Description
The manifold absolute pressure (MAP) sensor responds
to  changes  in  intake  manifold  pressure  (vacuum).    The
MAP  sensor  signal  voltage  to  the  powertrain  control
module (PCM) varies from below 2 volts at idle (high
vacuum) to above 4 volts with the key “ON,” engine not
running or at wide-open throttle (low vacuum).
The MAP sensor is used to determine manifold pressure
changes while the linear EGR flow test diagnostic is being
run  (refer  to 
DTC P0401),  to  determine  engine  vacuum
level  for  some  other  diagnostics  and  to  determine
barometric  pressure  (BARO).    The  PCM  monitors  the
MAP signals for voltages outside the normal range of the
MAP  sensor.    If  the  PCM  detects  a  MAP  signal  voltage
that is excessively high, DTC P0108 will be set.
Conditions for Setting the DTC
No TP sensor DTCs present.
Engine is running for more than 10 seconds.
Throttle position is below 3% if engine speed is below
1000 RPM.
Throttle position is below 10% if engine speed is above
1000 RPM.
The  MAP  sensor  indicates  an  intermittent  manifold
absolute pressure above 80kPa for a total of
approximately 10 seconds over a 16-second period.
Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.
The PCM will default to a BARO value of 79.3 kPa.
The  PCM  will  store  conditions  which  were  present
when  the  DTC  was  set  as  Freeze  Frame  and  in  the
Failure Records data.
Conditions for Clearing the MIL/DTC
DTC P0108 can be cleared by using the Tech 2 “Clear
Info”  function  or  by  disconnecting  the  PCM  battery
feed.
Diagnostic Aids
Check for the following conditions:
Poor connection at PCM – Inspect harness connectors
for  backed-out  terminals,  improper  mating,  broken
locks,  improperly  formed  or  damaged  terminals,  and
poor terminal-to-wire connection.
Damaged  harness  –  Inspect  the  wiring  harness  for
damage.  If the harness appears to be OK, observe the
MAP  display  on  the  Tech  2  while  moving  connectors
and wiring harnesses related to the sensor.  A change
in the display will indicate the location of the fault.
If  DTC  P0108  cannot  be  duplicated,  the  information
included  in  the  Failure  Records  data  can  be  useful  in
determining vehicle mileage since the DTC was last set. If
it  is  determined  that  the  DTC  occurs  intermittently,
performing the DTC P1108 Diagnostic Chart may isolate
the cause of the fault. 
Page 1253 of 6000

6E–136
ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0123 TP Sensor Circuit  High Voltage
D06RW028
Circuit Description
The throttle position (TP) sensor circuit provides a voltage
signal that changes relative to throttle blade angle.  The
signal  voltage  will  vary  from about  0.6  volts  at  closed
throttle to about 4.5 volts at wide open throttle (WOT).
The TP signal is one of the most important inputs used by
the powertrain control module (PCM) for fuel control and
many of the PCM-controlled outputs.
Conditions for Setting the DTC
The ignition is “ON.”
TP sensor signal voltage is greater than 4.88 volts for
a total of 0.78 second over a 1.5-second period.
Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.
The  PCM  will  store  conditions  which  were  present
when  the  DTC  was  set  as  Freeze  Frame  and  in  the
Failure Records data.
The PCM will use a default throttle position based on
mass air flow and RPM.
Conditions for Clearing the MIL/DTC
DTC P0123 can be cleared by using the Tech 2 “Clear
Info”  function  or  by  disconnecting  the  PCM  battery
feed.
Diagnostic Aids
Check for the following conditions:
Check intermittent codes.
The TP sensor shares a 5 Volt reference with the EGR
position  sensor.    Check  the  5  Volt  reference  if  these
DTCs are also set.
The  TP  sensor  shares  a  ground  with  the  IAT  sensor
and  the  EGR  position  sensor.    Check  the  ground  if
these other DTCs are also set.
Poor connection at PCM – Inspect harness connectors
for  backed-out  terminals,  improper  mating,  broken
locks,  improperly  formed  or  damaged  terminals,  and
poor terminal-to-wire connection.
Damaged  harness  –  Inspect  the  wiring  harness  for
damage.  If the harness appears to be OK, observe the
TP  sensor  display  on  the  Tech  2  while  moving
connectors  and  wiring  harnesses  related  to  the  TP
sensor.    A  change  in  the  display  will  indicate  the
location of the fault.
Faulty TP sensor – With the ignition key “ON,” engine
“OFF,”  observe  the  TP  sensor  display  on  the  Tech  2
while slowly depressing the accelerator to wide open
throttle.  If a voltage over 4.88 volts is seen at any point
in normal accelerator travel, replace the TP sensor.
If  DTC  P0123  cannot  be  duplicated,  the  information
included  in  the  Failure  Records  data  can  be  useful  in
determining vehicle mileage since the DTC was last set.
Test Description
Number  (s)  below  refer  to  the  step  number(s)  on  the
Diagnostic Chart.
7. Components that share the TP sensor 5 volt reference
“A” circuit include the following device:
EGR valve 
Page 1460 of 6000

6E–343 ENGINE DRIVEABILITY AND EMISSIONS
constant measuring and adjusting of the air/fuel ratio, the
fuel injection system is called a “closed loop” system.
The PCM monitors signals from several sensors in order
to  determine  the  fuel  needs  of  the  engine.  Fuel  is
delivered under one of several conditions called “modes.”
All modes are controlled by the PCM.
Fuel Pressure Regulator
The  fuel  pressure  regulator  is  a  diaphragm-operated
relief  valve  mounted  on  the  fuel  rail  with  fuel  pump
pressure on one side and manifold pressure on the other
side.    The  fuel  pressure  regulator  maintains  the  fuel
pressure  available  to  the  injector  at  three  times
barometric pressure adjusted for engine load.  It may be
serviced separate.
If the pressure is too low, poor performance and a DTC
P0131, DTC P0151,DTC P0171 or DTC P1171 will be the
result.  If the pressure is too high, excessive odor and/or a
DTC P0132, DTC P0152,DTC P0172 or DTC P0175 will
be  the  result.    Refer  to 
Fuel  System  Diagnosis for
information on diagnosing fuel pressure conditions.
0011
Fuel Pump Electrical Circuit
When the key is first turned “ON,” the PCM energizes the
fuel  pump  relay  for  two  seconds  to  build  up  the  fuel
pressure  quickly.    If  the engine  is  not  started within two
seconds, the PCM shuts the fuel pump off and waits until
the engine is cranked.  When the engine is cranked and
the 58 X crankshaft position signal has been detected by
the PCM, the PCM supplies 12 volts to the fuel pump relay
to energize the electric in-tank fuel pump.
An inoperative fuel pump will cause a “no-start” condition.
A fuel pump which does not provide enough pressure will
result in poor performance.
Fuel Rail
The  fuel  rail  is  mounted  to  the  top  of  the  engine  and
distributes  fuel  to  the  individual  injectors.    Fuel  is
delivered to the fuel inlet tube of the fuel rail by the fuel
lines.    The  fuel  goes  through  the  fuel  rail  to  the  fuel
pressure regulator.  The fuel pressure regulator maintainsa constant fuel pressure at the injectors.  Remaining fuel
is then returned to the fuel tank.
055RW009
Idle Air Control (IAC) Valve
The purpose of the idle air control (IAC) valve is to control
engine idle speed, while preventing stalls due to changes
in  engine  load.    The  IAC  valve,  mounted  in  the  throttle
body,  controls  bypass  air  around  the  throttle  plate.    By
moving the conical valve (pintle) in (to decrease air flow)
or out  (to increase air flow), a controlled amount of air can
move around the throttle plate.  If the RPM is too low, the
PCM  will  retract  the  IAC  pintle,  resulting  in  more  air
moving past the throttle plate to increase the RPM.  If the
RPM  is  too  high,  the  PCM  will  extend  the  IAC  pintle,
allowing  less  air  to  move  past  the  throttle  plate,
decreasing the RPM.
The IAC pintle valve moves in small steps called counts.
During  idle,  the  proper  position  of  the  IAC  pintle  is
calculated by the PCM based on battery voltage, coolant
temperature, engine load, and engine RPM.  If the RPM
drops  below  a  specified  value,    and  the  throttle  plate  is
closed, the PCM senses a near-stall condition. The PCM
will  then  calculate  a  new  IAC  pintle  valve  position  to
prevent stalls.
If the IAC valve is disconnected and reconnected with the
engine running, the idle RPM will be wrong.  In this case,
the IAC must be reset.  The IAC resets when the key is
cycled  “ON”  then  “OFF.”    When  servicing  the  IAC,  it
should  only  be  disconnected  or  connected  with  the
ignition “OFF.”
The position of the IAC pintle valve affects engine start-up
and the idle characteristics of the vehicle.  If the IAC pintle
is fully open, too much air will be allowed into the manifold.
This results in high idle speed, along with possible hard
starting  and  a  lean  air/fuel  ratio.    DTC  P0507  or  DTC
P1509 may set.  If the IAC pintle is stuck closed, too little
air will be allowed in the manifold.  This results in a low idle
speed, along with possible hard starting and a rich air/fuel
ratio.    DTC  P0506  or  DTC  P1508  may  set.    If  the  IAC
pintle is stuck part-way open, the idle may be high or low
and will not respond to changes in the engine load. 
Page 1968 of 6000

6E–75 4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0123 (Flash DTC 21)
 AP Sensor High Voltage
060RW134
Circuit Description
The  accelerator  position  (AP)  sensor  circuit  provides  a
voltage  signal  that  changes  relative  to  throttle  blade
angle.
The TP signal is one of the most important inputs used by
the Engine Control Module ECM for fuel volume control
and many of the ECM-controlled outputs.
Action Taken When the DTC Sets
The  ECM  will  store  conditions  which  were  present
when  the  DTC  was  set  as  Freeze  Frame  and  in  the
Failure Records data.
Conditions for Clearing the MIL/DTC
DTC P0123 can be cleared by using the Tech 2 “Clear
Info”  function  or  by  disconnecting  the  ECM  battery
feed.
Diagnostic Aids
Check for the following conditions:
Poor connection at ECM – Inspect harness connectors
for  backed-out  terminals,  improper  mating,  brokenlocks,  improperly  formed  or  damaged  terminals,  and
poor terminal-to-wire connection.
Damaged  harness  –  Inspect  the  wiring  harness  for
damage.  If the harness appears to be OK, observe the
AP  sensor  display  on  the  Tech  2  while  moving
connectors  and  wiring  harnesses  related  to  the  TP
sensor.    A  change  in  the  display  will  indicate  the
location of the fault.
Faulty AP sensor – With the ignition key “ON,” engine
“OFF,”  observe  the  AP  sensor  display  on  the  Tech  2
while slowly depressing the accelerator to wide open
throttle.  If a voltage over 4.88 volts is seen at any point
in normal accelerator travel, replace the AP sensor.
If  DTC  P0123  cannot  be  duplicated,  the  information
included  in  the  Failure  Records  data  can  be  useful  in
determining vehicle mileage since the DTC was last set.
Test Description
Number  (s)  below  refer  to  the  step  number(s)  on  the
Diagnostic Chart.
8. Components that share the AP sensor 5 volt reference
“A” circuit include the following device: 
Page 2039 of 6000

6E–146
4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P1486 (Flash DTC 74) 
ITP (Intake Throttle Position) Sensor High Voltage
060RW134
Circuit Description
The intake throttle position (ITP) sensor circuit provides a
voltage  signal  that  changes  relative  to  throttle  blade
angle.
Action Taken When the DTC Sets
The ECM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.
The  ECM  will  store  conditions  which  were  present
when  the  DTC  was  set  as  Freeze  Frame  and  in  the
Failure Records data.
Conditions for Clearing the MIL/DTC
DTC P1486 can be cleared by using the Tech 2 “Clear
Info”  function  or  by  disconnecting  the  ECM  battery
feed.
Diagnostic Aids
Check for the following conditions:
Poor connection at ECM – Inspect harness connectors
for  backed-out  terminals,  improper  mating,  broken
locks,  improperly  formed  or  damaged  terminals,  and
poor terminal-to-wire connection.
Damaged  harness  –  Inspect  the  wiring  harness  for
damage.  If the harness appears to be OK, observe the
ITP  sensor  display  on  the  Tech  2  while  moving
connectors  and  wiring  harnesses  related  to  the  TP
sensor.    A  change  in  the  display  will  indicate  the
location of the fault.
Faulty TP sensor – With the ignition key “ON,” engine
“OFF,”  observe  the  TP  sensor  display  on  the  Tech  2
while slowly depressing the accelerator to wide open
throttle.
If  DTC  P1486  cannot  be  duplicated,  the  information
included  in  the  Failure  Records  data  can  be  useful  in
determining vehicle mileage since the DTC was last set. 
Page 2992 of 6000

WIRING SYSTEM 8D–399
1. Check to see if the battery voltage is normal.
2. Check to see if the fuse is normal.
3. Replace the anti–theft & keyless entry control unit with one reserved for test. If a trouble recurs even after replacing
the control unit, find out the cause of the trouble by referring to “System check procedure” and the following list.
ITEM MALFUNCTION POSSIBLE CAUSE DETECTING METHOD REMARKS
ANTI–THEFT
indicator light
does not flash
ANTI–THEFT
indicator light
does not turn off.
(Steadily on)
When door is
opened by pulling
up locking knob,
alarm does not
operate
Alarm does not
stop. Indicator light
does not change
to fully ON
condition, or does
not come on at
all.Burnt out indicator
light bulb possible.
Refer to “Connector
check table” in this
system.
Refer to “Connector
check table” in this
system.
Refer to “Connector
check table” in this
system.
Refer to “Connector
check table” in this
system.
Refer to “Connector
check table” in this
system.
Refer to “Connector
check table” in this
system. Defective contact of door switch,
or open circuit in door switch
wiring.
Short circuit in the detect switch.
Engine hood, doors and tailgate
are not fully closed and locked.
Defective door switch, or short
circuit in switch wiring.
Defective tamper switch, or short
circuit in wiring.
Defective lock switch, or short
circuit in wiring.
Defective engine hood switch, or
short circuit in wiring.
Defective tailgate switch, or short
circuit in wiring.
Defective control unit.
Poor contact of lock switch, or
open circuit in wiring.
Broken wire in wiring to headlight
and horn, or a blown fuse.
Defective contact of detect
switch, or damaged switch wiring.With door open, dome light and
courtesy light do not come on.
Check the control unit connector.
Check to see if doors are closed
and locked.
Dome light and courtesy light
remain lit on after closing doors.
Check the control unit connector.
Check the control unit connector.
Check the control unit connector.
Luggage room light remains lit
after closing tailgate.
Check alarm operation (See No.
46 of “System check procedure”),
possible cause is a poor contact
of lock switch of an open circuit in
wiring.
Check to see if headlights go out.
Check the control unit connector.
Check the control unit connector. A
C
D
E B 
Page 3366 of 6000

SECURITY AND LOCKS8H–27
StepNo Ye s Action
41. Lock the door and unlock it three times.
2. Close the door and then open it.
NOTE: This step must be performed within ten seconds after step
3.
Is the action complete?
Go to Step 5Finished
5Answer back mode changes.
Is this step complete?
Go to Step 6Go to Step 7
6The control unit makes lock/unlock response once with interval of
one second.
Is the response complete?
Finished—
7The  control  unit  makes  lock/unlock  response  three  times  with
interval of one second.
Is the response complete?
Finished—
Anti–theft & Keyless Entry Control
Unit/Transmitter Replacement
Anti–theft & Keyless Entry Control Unit
Replacement
1. Remove and install the control unit.
Refer  to  Anti–theft  &  Keyless  Entry  Control  Unit
Removal and Installation in this section.
2. Register ID code.
Refer to ID Code Registration in this section.
3. Check that the keyless entry system works normally.
Transmitter Replacement
1. Prepare a new transmitter.
2. Regiter ID code.
Refer to ID Code Registration in this section.
3. Check that the keyless entry system works normally.
Transmitter Battery Replacement
1. Remove a screw to remove the cover.
2. Remove the batteries.
3. Set the new batteries into the transmitter.
4. Install the cover to the transmitter.
5. Check that the keyless entry system works normally. 
Page 4772 of 6000

6E–115 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0108 MAP Sensor Circuit High Voltage
D06RW102
Circuit Description
The manifold absolute pressure (MAP) sensor responds
to  changes  in  intake  manifold  pressure  (vacuum).    The
MAP  sensor  signal  voltage  to  the  powertrain  control
module (PCM) varies from below 2 volts at idle (high
vacuum) to above 4 volts with the key “ON,” engine not
running or at wide-open throttle (low vacuum).
The MAP sensor is used to determine manifold pressure
changes while the linear EGR flow test diagnostic is being
run  (refer  to 
DTC P0401),  to  determine  engine  vacuum
level  for  some  other  diagnostics  and  to  determine
barometric  pressure  (BARO).    The  PCM  monitors  the
MAP signals for voltages outside the normal range of the
MAP  sensor.    If  the  PCM  detects  a  MAP  signal  voltage
that is excessively high, DTC P0108 will be set.
Conditions for Setting the DTC
No TP sensor DTCs present.
Engine is running for more than 10 seconds.
Throttle position is below 3% if engine speed is below
1000 RPM.
Throttle position is below 10% if engine speed is above
1000 RPM.
The  MAP  sensor  indicates  an  intermittent  manifold
absolute pressure above 80kPa for a total of
approximately 10 seconds over a 16-second period.
Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.
The PCM will default to a BARO value of 79.3 kPa.
The  PCM  will  store  conditions  which  were  present
when  the  DTC  was  set  as  Freeze  Frame  and  in  the
Failure Records data.
Conditions for Clearing the MIL/DTC
DTC P0108 can be cleared by using the Tech 2 “Clear
Info”  function  or  by  disconnecting  the  PCM  battery
feed.
Diagnostic Aids
Check for the following conditions:
Poor connection at PCM – Inspect harness connectors
for  backed-out  terminals,  improper  mating,  broken
locks,  improperly  formed  or  damaged  terminals,  and
poor terminal-to-wire connection.
Damaged  harness  –  Inspect  the  wiring  harness  for
damage.  If the harness appears to be OK, observe the
MAP  display  on  the  Tech  2  while  moving  connectors
and wiring harnesses related to the sensor.  A change
in the display will indicate the location of the fault.
If  DTC  P0108  cannot  be  duplicated,  the  information
included  in  the  Failure  Records  data  can  be  useful  in
determining vehicle mileage since the DTC was last set. If
it  is  determined  that  the  DTC  occurs  intermittently,
performing the DTC P1108 Diagnostic Chart may isolate
the cause of the fault. 
Page 4793 of 6000

6E–136
ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0123 TP Sensor Circuit  High Voltage
D06RW028
Circuit Description
The throttle position (TP) sensor circuit provides a voltage
signal that changes relative to throttle blade angle.  The
signal  voltage  will  vary  from about  0.6  volts  at  closed
throttle to about 4.5 volts at wide open throttle (WOT).
The TP signal is one of the most important inputs used by
the powertrain control module (PCM) for fuel control and
many of the PCM-controlled outputs.
Conditions for Setting the DTC
The ignition is “ON.”
TP sensor signal voltage is greater than 4.88 volts for
a total of 0.78 second over a 1.5-second period.
Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.
The  PCM  will  store  conditions  which  were  present
when  the  DTC  was  set  as  Freeze  Frame  and  in  the
Failure Records data.
The PCM will use a default throttle position based on
mass air flow and RPM.
Conditions for Clearing the MIL/DTC
DTC P0123 can be cleared by using the Tech 2 “Clear
Info”  function  or  by  disconnecting  the  PCM  battery
feed.
Diagnostic Aids
Check for the following conditions:
Check intermittent codes.
The TP sensor shares a 5 Volt reference with the EGR
position  sensor.    Check  the  5  Volt  reference  if  these
DTCs are also set.
The  TP  sensor  shares  a  ground  with  the  IAT  sensor
and  the  EGR  position  sensor.    Check  the  ground  if
these other DTCs are also set.
Poor connection at PCM – Inspect harness connectors
for  backed-out  terminals,  improper  mating,  broken
locks,  improperly  formed  or  damaged  terminals,  and
poor terminal-to-wire connection.
Damaged  harness  –  Inspect  the  wiring  harness  for
damage.  If the harness appears to be OK, observe the
TP  sensor  display  on  the  Tech  2  while  moving
connectors  and  wiring  harnesses  related  to  the  TP
sensor.    A  change  in  the  display  will  indicate  the
location of the fault.
Faulty TP sensor – With the ignition key “ON,” engine
“OFF,”  observe  the  TP  sensor  display  on  the  Tech  2
while slowly depressing the accelerator to wide open
throttle.  If a voltage over 4.88 volts is seen at any point
in normal accelerator travel, replace the TP sensor.
If  DTC  P0123  cannot  be  duplicated,  the  information
included  in  the  Failure  Records  data  can  be  useful  in
determining vehicle mileage since the DTC was last set.
Test Description
Number  (s)  below  refer  to  the  step  number(s)  on  the
Diagnostic Chart.
7. Components that share the TP sensor 5 volt reference
“A” circuit include the following device:
EGR valve 
Page 5000 of 6000

6E–343 ENGINE DRIVEABILITY AND EMISSIONS
constant measuring and adjusting of the air/fuel ratio, the
fuel injection system is called a “closed loop” system.
The PCM monitors signals from several sensors in order
to  determine  the  fuel  needs  of  the  engine.  Fuel  is
delivered under one of several conditions called “modes.”
All modes are controlled by the PCM.
Fuel Pressure Regulator
The  fuel  pressure  regulator  is  a  diaphragm-operated
relief  valve  mounted  on  the  fuel  rail  with  fuel  pump
pressure on one side and manifold pressure on the other
side.    The  fuel  pressure  regulator  maintains  the  fuel
pressure  available  to  the  injector  at  three  times
barometric pressure adjusted for engine load.  It may be
serviced separate.
If the pressure is too low, poor performance and a DTC
P0131, DTC P0151,DTC P0171 or DTC P1171 will be the
result.  If the pressure is too high, excessive odor and/or a
DTC P0132, DTC P0152,DTC P0172 or DTC P0175 will
be  the  result.    Refer  to 
Fuel  System  Diagnosis for
information on diagnosing fuel pressure conditions.
0011
Fuel Pump Electrical Circuit
When the key is first turned “ON,” the PCM energizes the
fuel  pump  relay  for  two  seconds  to  build  up  the  fuel
pressure  quickly.    If  the engine  is  not  started within two
seconds, the PCM shuts the fuel pump off and waits until
the engine is cranked.  When the engine is cranked and
the 58 X crankshaft position signal has been detected by
the PCM, the PCM supplies 12 volts to the fuel pump relay
to energize the electric in-tank fuel pump.
An inoperative fuel pump will cause a “no-start” condition.
A fuel pump which does not provide enough pressure will
result in poor performance.
Fuel Rail
The  fuel  rail  is  mounted  to  the  top  of  the  engine  and
distributes  fuel  to  the  individual  injectors.    Fuel  is
delivered to the fuel inlet tube of the fuel rail by the fuel
lines.    The  fuel  goes  through  the  fuel  rail  to  the  fuel
pressure regulator.  The fuel pressure regulator maintainsa constant fuel pressure at the injectors.  Remaining fuel
is then returned to the fuel tank.
055RW009
Idle Air Control (IAC) Valve
The purpose of the idle air control (IAC) valve is to control
engine idle speed, while preventing stalls due to changes
in  engine  load.    The  IAC  valve,  mounted  in  the  throttle
body,  controls  bypass  air  around  the  throttle  plate.    By
moving the conical valve (pintle) in (to decrease air flow)
or out  (to increase air flow), a controlled amount of air can
move around the throttle plate.  If the RPM is too low, the
PCM  will  retract  the  IAC  pintle,  resulting  in  more  air
moving past the throttle plate to increase the RPM.  If the
RPM  is  too  high,  the  PCM  will  extend  the  IAC  pintle,
allowing  less  air  to  move  past  the  throttle  plate,
decreasing the RPM.
The IAC pintle valve moves in small steps called counts.
During  idle,  the  proper  position  of  the  IAC  pintle  is
calculated by the PCM based on battery voltage, coolant
temperature, engine load, and engine RPM.  If the RPM
drops  below  a  specified  value,    and  the  throttle  plate  is
closed, the PCM senses a near-stall condition. The PCM
will  then  calculate  a  new  IAC  pintle  valve  position  to
prevent stalls.
If the IAC valve is disconnected and reconnected with the
engine running, the idle RPM will be wrong.  In this case,
the IAC must be reset.  The IAC resets when the key is
cycled  “ON”  then  “OFF.”    When  servicing  the  IAC,  it
should  only  be  disconnected  or  connected  with  the
ignition “OFF.”
The position of the IAC pintle valve affects engine start-up
and the idle characteristics of the vehicle.  If the IAC pintle
is fully open, too much air will be allowed into the manifold.
This results in high idle speed, along with possible hard
starting  and  a  lean  air/fuel  ratio.    DTC  P0507  or  DTC
P1509 may set.  If the IAC pintle is stuck closed, too little
air will be allowed in the manifold.  This results in a low idle
speed, along with possible hard starting and a rich air/fuel
ratio.    DTC  P0506  or  DTC  P1508  may  set.    If  the  IAC
pintle is stuck part-way open, the idle may be high or low
and will not respond to changes in the engine load.