1988 PONTIAC FIERO change time

6E3-B-4 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
LACK OF POWER, SLUGGISH, OR SPONGY
Definition: Engine delivers less than expected power. Little or
no increase in speed when accelerator pedal is pushed down part way.
@ Perform careful visual check as described at
start of Section "B".
@ Compare customer's car to similar unit.
Make sure the customer's car has an actual
problem.
@ Remove air cleaner and check air filter for
dirt, or for being plugged. Replace as
necessary.
@ CHECK:
- For loose or leaking air duct between MAF
sensor and throttle body.
- Ignition timing. See emission control
information label.
- Restricted fuel filter, contaminated fuel or
improper fuel pressure. See CHART A-7.
- ECM Ground circuits - See ECM wiring
diagrams.
- EGR operation for being open, or partly open
all the time
- CHART C-7.
- Exhaust system for possible restriction: See
CHART
B-1.
- Inspect exhaust system for damaged or
collapsed pipes.
- Inspect muffler for heat distress or possible
internal failure.
- For possible plugged catalytic convertor by
comparing exhaust system backpressure on
each side at engine. Check backpressure by
removing
A.1.R check valves near exhaust
manifolds. See CHART
B-1 for procedure.
- Generator output voltage. Repair if less than 9
or more than 16 volts.
- Engine valve timing and compression.
- Engine for proper or worn camshaft. See Section
"6A".
- Secondary voltage using a shop ocilliscope or a
spark tester
5-26792 (ST-125) or equivalent.
- Check for excessive knock retard. See CHART
C-5.
DETONATION ISPARK KNOCK
Definition: A mild to severe ping, usually worse under
acceleration. The engine makes sharp metallic knocks that
change with throttle opening. Sounds like popcorn popping.
@ Check for obvious overheating problems:
- Low coolant.
- Loose water pump belt.
- Restricted air flow to radiator, or restricted
water flow thru radiator.
- Inoperative electric cooling fan circuit. See
CHART C-12.
@ CHECK:
- Ignition timing. See vehicle emission control
information label.
- EGR system for not opening - CHART C-7.
- TCC operation - CHART C-8.
- Fuel system pressure. See CHART A-7.
- Mem-Cal - Be sure it's the correct one. (See
"Service Bulletins").
- Valve oil seals for leaking.
@ Check for incorrect basic engine parts such as
cam, heads, pistons, etc.
@ Checkforpoorfuelquality.
@ Remove carbon with top engine cleaner. Follow
instructions on can.
@ Check ESC system
See CHART C-5
@ To help determine if the condition is caused by a
rich or lean system, the car should be driven at
the speed of the complaint. Monitoring block
learn at the complaint speed will help identify the
cause of the
problem. If the system is runnig lean
(block learn greater than
1381, refer to
"Diagnostic Aids" on facing page of Code
44. If
the system is running rich (block learn less than
1181, refer to "Diagnostic Aids" on facing page of
Code 45.

DRIVEABILITY AND EMISSIONS S.OL (VIN F) & 5.7L (VIN 8) 6E3-B-5
Definition: Steady pulsation or jerking that follows engine
speed, usually more pronounced as engine load increases. The
exhaust has
a steady spitting sound at idle or low speed.
@ Perform careful visual check as described at blink
at any connector, it is a faulty injector drive
start of Section
"B". circuit harness, connector, or terminal.
@ Check for missing cylinder by: @ Perform the Injector Balance Test. See CHART
1. Disconnect IAC valve. Start engine. C-2A.
Remove one spark plug wire at a time
@ CHECK:
using insulated pliers. - Spark plug wires by connecting ohmmeter to
2. If there is an rpm drop on all cylinders ends
of each wire in question. If meter reads over
(equal to within
50 rpm), go to "ROUGH, 30,000
ohms, replace wire(s).
UNSTABLE, OR INCORRECT IDLE, - Fuel System - Plugged fuel filter, water, low
STALLING" symptom. Reconnect IAC pressure. See CHART A-7.
valve.
- Valve timing.
3. If there is no rpm drop on one or more - Secondary voltage using a shop ocilliscope or a
cylinders, or excessive variation in drop, spark tester 5-26792 (ST-125)
or equivalent.
check for spark on the suspected
@ Visually inspect distributor cap and rotor for
cylinder(s) with J 26792 (ST-125) Spark moisture, dust, cracks, burns, etc. Spray cap and
Gap Tool or equivalent. If no spark, see plug wires with fine water mist to check for
Section 6D for Intermittent Operation or shorts.
Miss. If there is spark, remove spark
@ A miss condition can be caused by EM1
plug(s) in these cylinders and check for: (Electromagnetic Interference) on the reference
- Cracks circuit. EM1 can usually be detected by
- Wear monitoring engine rpm with a "Scan" tool. A
- Improper Gap sudden
increase in rpm with little change in
- Burned Electrodes actual engine rpm change, indicates EM1 is
- Heavy Deposits present.
@ Perform compression check on questionable If
the problem exists, check routing of secondary
cylinder(s) found above. If compression is low, wires, check
all distributor ground circuits.
repair as necessary. See Section
"6". @ Remove rocker covers. Check for bent pushrods,
@ Disconnect all injector harness connectors. worn
rocker arms, broken valve springs, worn
Connect
5-34730-2 Injector Test Light or camshaft
lobes. Repair as necessary. See Section
equivalent 6 volt test light between the
"6A".
harness terms, of each injector connector and
note light while cranking. If test light fails to
BACKFIRE
Definition: Fuel ignites in intake manifold, or
in exhaust system, making a loud popping noise.
@ CHECK: - Spark plugs for crossfire also inspect (distributor
- Loose wiring connector or air duct at MAF
cap, spark plug wires, and proper routing of plug
sensor. wires).
- Compression - Look for sticking or leaking - Ignition system for intermittent condition. (See
valves. Section
"6D").
- EGR operation for being open all the time. See - Engine timing - see emission control information
CHART C-7. label.
- EGR gasket for faulty or loose fit. - Perform fuel system diagnosis check, CHART A-
- Valve timing. 7A.
- Output voltage of ignition coil using a shop - Perform injector balance test CI-IART C-2A.
ocilliscope or spark tester 5-26792 (ST-125) or
- A.I.R. system check valves - See Section "C-6".
equivalent.

6E3-61-2 S.OL (VIM F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
The ECM controls output circuits such as the
injector, IAC, cooling fan relay, etc. by controlling the
ground circuit through transistors in the ECM.
INFORMATION SENSORS
Engine Coolant Temperature Sensor
(Figure
Cl-2)
The coolant sensor is a thermistor (a resistor which
changes value based on temperature) mounted in the
engine coolant stream. Low coolant temperature
produces a high resistance (100,000 ohms at
-4O0C/-
40°F), while high temperature causes low resistance
(70 ohms at
130°C/266"F).
The ECM supplies a 5-volt signal to the coolant
sensor through
a resistor in the ECM and measures
the voltage. The voltage will be high when the engine
is cold, and low when the engine is hot. By measuring
the voltage, the ECM knows the engine coolant
temperature. Engine coolant temperature affects
most systems the
ECM controls.
A failure in the coolant sensor circuit should set
either a Code 14 or Code
15. Remember, these codes
indicate
a failure in the coolant temperature circuit,
so proper use of the chart will lead to either repairing
a wiring problem or replacing the sensor, to properly
repair
a problem.
ENGINE COOLANT TEMPERATURE SENSOR
HARNESS CONNECTOR TO
ECM
4-2-85 LOCKING TAE
Figure C1-2 - Engine Coolant Temperature Sensor
Mass Air Flow (MAF) Sensor
(Figure
C1-3)
The mass air flow (MAF) sensor measures the
amount of air which passes through it.
'l'he ECM uses
this information to determine the operating condition
of the engine, to control fuel delivery.
A large
quantity of air indicates acceleration, while a small
quantity indicates deceleration or idle.
The Bosch mass air flow
(MAF) sensor used in this
vehicle is of the hot wire type. Current is supplied to
the sensing wire to maintain a calibrated
temperature, and as air flow increases or decreases
the current will vary. This varying
of current causes a voltage drop within
the meter circuitry which isdirectly proportional to air
mass. The ECM supplies a current limiting 5-volt
source on the signal line, and the MAF sensor pulls
the voltage low (about
.4V) with low air flow and up to
about 5 volts with high air flow such as
WOT. The
voltage drop is then processed by the ECM for
calculating fuel delivery. If the sensor fails, a Code 33
or 34 should be stored in memory.
Due to the sensor's hot wire being exposed to air,
which always contains some contaminants, there can
be deposits form on the sensing wire. This can affect
the accuracy of the meters measurement. To keep the
system functioning properly, the wire is heated to
about
1000°F after engine shut down. This burn-off
cycle is controlled by the ECM, which energizes the
burn-off relay. The ECM will ground the relay
winding after engine shut down, if the engine had
been running a specified amount of time. With the
relay energized, the ECM then monitors the MAF
signal line to determine if the burn-off function took
place. If it didn't, then a Code 36 will be stored and the
"Service Engine Soon" light will come
"ON" the next
time the engine is started.
Figure C1-3 - Mass Air Flow (MAF) Sensor
Manifold Air Temperature (MAT) Sensor
The air temperature sensor (MAT) is a thermistor
(a resistor which changes value based on temperature)
is mounted in the plenum.
Low temperature produces
a high resistance (100,000 ohms at
-40°C/-40°F) while
high temperature causes low resistance (70 ohms at
130°C/266"F).
The ECM supplies a 5-volt signal to the sensor
through a resistor in the ECM and measures the
voltage. 'l'he voltage will be high when the manifold
air is cold, and low when the air is hot. By measuring
the voltage, the ECM knows the manifold air
temperature

6E3-C2-2 5.OL (VIN F) & 5.7L(VIN 8) DRIVEABILITY AND EMISSIONS
MODES OF OPERATION
The ECM looks at voltages from several sensors to
determine how much fuel to give the engine. The fuel
is delivered under one of several conditions, called
"modes". All the modes are controlled by the ECM
and are described below.
Starting Mode
When the ignition is first turned "ON", the ECM
will turn "ON" the fuel pump relay for two seconds,
and the fuel pump will build up pressure. The ECM
then checks the coolant temperature sensor, throttle
position sensor, and determines the proper airlfuel
ratio for starting. This ranges from 1.5
: 1 at -36°C
(-33°F) to 14.7:l at 94°C (201°F). The ECM controls
the amount of fuel delivered in the starting mode by
changing how long the injectors are pulsed "ON".
The cold start valve
(Figure C2-2), not controlled
by the ECM, is used to provide additional fuel during
the starting mode to improve cold start-ups. This
circuit is important, when the engine coolant
temperature is very low, because the other injectors
would not be pulsed "ON" long enough to provide the
needed amount of fuel to start. The cold start valve is
somewhat different from the other injectors in that it
causes the fuel to be vaporized for a better combustible
mixture.
The circuit is activated only in the crank mode.
The power is supplied directly from the starter
solenoid and is protected by the crank fuse. The
system is controlled by a cold start fuel injection
switch which provides a ground path for the valve
during cranking whenever engine coolant is below
35"
C (95°F).
100 VALVE - COLD START
101 TUBE AND BODY ASSEMBLY
102 O-RING SEAL
- VALVE
103 O-RING SEAL
- BODY
104 O-RING SEAL -TUBE
The cold start fuel injection switch contains a
bimetal switch which opens the circuit at specified
coolant temperature. This bimetal is also heated
by
the winding in the switch, which would allow the
valve to stay "ON" 8 seconds at
-20" C or below. The
time the switch stays closed varies inversely with
coolant temperature. In other words, as the coolant
temperature goes up the maximum cold start valve
"ON" time goes down.
Clear Flood Mode
If the engine floods, clear it by pushing the
accelerator pedal down all the way. The ECM then
pulses the injectors at an airlfuel ratio of
20:l. The
ECM holds this injector rate as long as the throttle
stays wide open, and the engine rpm is below 600.
If
the throttle position becomes less than 80%, the ECM
returns to the starting mode.
Run Mode
The RUN mode has two conditions called "Open
Loop" and "Closed Loop".
When the engine is first started, and rpm is above
400 rpm, the system goes into "Open Loop" operation.
In "Open Loop", the ECM will ignore the signal from
the Oxygen
(Oz) sensor, and calculate the airlfuel
ratio based on inputs from the coolant and MAF
sensors.
The system will stay in
"Open Loop" until the
following conditions are met:
1. The O2 sensor has varying voltage output,
showing that it is hot enough to operate properly.
(This depends on temperature.)
2. The coolant sensor is above a specified
temperature about 40°C
(104°F).
3. A specific amount of time has elapsed after
starting the engine.
The specific values for the above conditions vary
with different engines, and are stored in the mem-cal.
When these conditions are met, the system goes into
"Closed Loop" operation. In "Closed Loop", the ECM
will calculate the airlfuel ratio (injector on-time)
based on the signal from various sensors but
mainly
the O2 sensor. This allows the air 1 fuel ratio to stay
very close to 14.7: 1
.
Acceleration Mode
The ECM looks at rapid changes in throttle
position and air flow, and provides extra fuel.
Figure C2-2 Cold Start Valve

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-CZ-3
Deceleration Mode
The ECM looks at changes in throttle position and
air flow to reduce the amount of fuel. When
deceleration is very fast, the ECM may shut off fuel
completely for short periods.
Battery Voltage Correction Mode
When battery voltage is low, the ECM can
compensate for the weak spark delivered by the
distributor by:
@ Increasing the amount of fuel delivered;
@ Increasing the idle rpm; and
@ Increasing ignition dwell time.
Fuel Cutoff Mode
No fuel is delivered by the injector when the
ignition is "OFF". This prevents dieseling. Also, fuel
is not delivered if no reference pulses are seen from
the distributor, which means the engine is not
running. This prevents flooding.
FUEL CONTROL SYSTEM
Basic System Operation
The fuel system (Figure C2-3) starts with the fuel
in the fuel tank.
An electric fuel pump, located in the fuel tank with
the gage sending unit, pumps
fuel to the fuel rail
through an in-line fuel filter. The pump is designed to
provide fuel at a pressure above the pressure needed
by the injectors. A pressure regulator in the fuel rail
keeps fuel available to the injectors at
a constant
pressure, depending on manifold pressure. Unused
fuel is returned to the fuel tank by a separate line. For
further information on the fuel tank, in-line filter, and
fuel lines, see Section
"6C".
The injectors are controlled by the ECM. They
deliver fuel in one of several modes, as described
above. In order to properly control the fuel supply, the
fuel pump is operated by the
ECM through the fuel
pump relay and oil pressure switch (see Fuel Pump
Electrical Circuit Code
54).
Throttle Body Unit
The throttle body has a throttle valve to control
the amount of air delivered to the engine. The TPS
and the IAC valve are also mounted on the throttle
body. The throttle body contains vacuum ports located
at, above, or below the
throttIe valve. 'I'hese ports
generate the vacuum signals
needed I,y v~irious
Figure C2-3 Fuel System
components. Engine coolant is directed through the
coolant cavity, on the bottom of the throttle body, to
warm the throttle valve and prevent icing.
Fuel Rail
The fuel rail is mounted to the top of the engine. It
distributes fuel to the individual injectors. Fuel is
delivered to the input end of the rail by the fuel lines,
goes through the rail, then to the pressure regulator.
Remaining fuel is then returned to the fuel tank.
Fuel Injectors
The fuel injector is a solenoid operated device
controlled by the ECM (see Figure
C2-4). The ECM
turns
"ON" the solenoid, which opens a valve to allow
fuel delivery.
The fuel, under pressure, is injected in a
conical spray pattern at the opening of the intake
valve. The fuel, which is not used by the injectors,
passes through the pressure regulator before being
returned to the fuel tank.
An injector which is stuck partly open will cause
loss of pressure after engine shut down, so long crank
times would be noticed on some engines. Also,
dieseling could occur because some fuel could be
delivered to the engine after the ignition is turned
"OFF".

6E3-CZ-4 5.OL (VIN F) & 5.7L(VIN 8) DRIVEABILITY AND EMISSIONS
FUEL INJECTOR
1 INTAKE MANIFOLD
( INTAKE VALVE
1 ELECTRICAL TERMINAL
Figure C2-4 Fuel Injector
Pressure Regulator
The pressure regulator is a diaphragm-operated
relief valve with injector pressure on one side and
manifold pressure on the other. The function of the
regulator is to maintain a constant pressure at the
injector at all times. The pressure regulator
cotnpensates for engine load by increasing fuel
pressure when it sees low engine vacuum.
The pressure regulator is mounted on the fuel rail,
and is serviced separately.
If the pressure
is too low, poor performance could
result. If the pressure is too high, excessive odor and a
Code
45 may result. CHART A-7 has information on
diagnosing fuel pressure conditions.
Idle Air Control (IAC) Valve
The purpose of the idle air control (IAC) valve
(shown in Figure
C2-5) 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
valve. Hy
moving a conical valve IN (to decrease air flow) or
OUT (to increase air flow), a controlled amount of air
can move around the throttle plate. If rpm is too low.
more air
is bypassed around the throttle valve to
increase rpm. If
rpm is too high, less air is bypassed around the
throttle valve to decrease rpm.
The IAC valve moves in small steps called
"counts", which can be monitored by a "Scan" tool.
During idle, the proper position of the IAC valve is
calculated by the ECM based on battery voltage,
coolant temperature, and engine rpm. If the rpm
drops below
a specified rpm, and the throttle plate is
closed, the ECM senses a near stall condition. The
ECM will then calculate a new valve position to
prevent stalls.
If the IAC valve is disconnected and reconnected
with the engine running, the idle rpm may be wrong.
In this case, the IAC valve can be reset by starting the
engine momentarily and then turning the ignition
"OFF
".
When servicing the IAC, it should only be
disconnected or connected with the ignition "OFF".
This will keep from having to reset the IAC.
The IAC valve affects only the idle characteristics
of the vehicle. If it is open fully, too much air will be
allowed into the manifold and idle speed will be high.
If it is stuck closed, too little air will be allowed in the
manifold, and idle speed will be too low. If it is stuck
part way open, the idle may be rough, and will not
respond to engine load changes.
Different designs are used for the IAC valve. Be
sure to use the correct design when replacement is
required.
SINGLE TAPER VALVE
DUAL TAPER VALVE
BLUNT
PINTLE
Figure C2-5 IAC Valve Designs

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-C2-5
Fuel Pump Electrical Circuit
When the ignition is first turned "ON", without
the engine running, the ECM will turn the fuel pump
relay "ON" for two seconds.
This builds up the fuel
pressure quickly. If the engine is not started within
two seconds, the ECM will shut the fuel pump "OFF"
and wait until the engine is cranking. As soon as the
engine is cranked, the ECM will turn the relay "ON"
and run the fuel pump.
As
a backup system to the fuel pump relay, the
fuel pump can also be turned "ON" by the oil pressure
switch. The oil pressure switch is a normally open
switch which closes when oil pressure reaches about
28
kPa (4 psi). If the fuel pump relay fails, the oil
pressure switch will close, and run the fuel pump.
An inoperative fuel pump relay can result in long
cranking times, particularly if the engine is cold but
should result in
a Code 54.
An inoperative fuel pump would cause a no start
condition. A fuel pump which does not provide enough
pressure can result in poor performance.
DIAGNOSIS
FUEL CONTROL SYSTEM
Some failures of this system will result in an
"Engine Cranks But Won't Run". If
this condition
exists see CHART A-3. This chart will determine if
the problem is caused by the ignition system, ECM, or
fuel pump circuit. If
it's determined to be a fuel
problem CHART A-7 will be used. This includes the
injectors, pressure regulator, fuel pump, and fuel
pump relay. The fuel system wiring schematic is
covered on the facing page of Code CHART 54.
If a malfunction occurs in the fuel control system,
it usually results in either a rich or
a lean exhaust
condition. This condition is sensed by the oxygen
sensor and the ECM will change the fuel calculation
(injector pulse width) based on the
O2 sensor reading.
The change
made to the fuel calculation will be
indicated by a change in the block learn values, which
can be monitored by a "Scan" tool.
The normal block
learn values are around 128, and if the
O2 sensor is
sensing a lean condition, the EC
M will add fuel which
will result in a block learn value above 128.
If the O2
sensor is sensing a rich exhaust the ECM will reduce
fuel to the engine and this will result in block learn
values below 128. Some variations in block
learn
values are normal because all engines are not exactly
the same. However, if the block learn values are
+ 10
counts from 128 a system problem exists. If the block
learn values are greater than 138 see Code 44, for
items which can cause a lean system.
If the block learn values are less than 118 see Code
45 for items which can cause the system to run rich. If
a driveability symptom exists, refer to the
particular symptom in Section
"B" for additional
items to check.
IDLE AIR CONTROL VALVE
AUScan" tool will read IAC position in steps (counts).
"0" steps indicates the ECM is commanding the IAC to
be driven all the way in, to a fully seated position, and
this is usually caused by a vacuum leak. The higher
the number of counts the more air being allowed to
pass the IAC valve. CHART C-2C can be used to
diagnosis the IAC valve. Also refer to "Rough,
Unstable, or Incorrect Idle, Stalling" in symptoms,
Section "B" for other possibilities for the cause
of idle
problems.
FUEL SYSTEM PRESSURE TEST
A fuel system pressure test is part of several of the
diagnostic charts and symptom checks. To perform
this test, use the procedure in CHART A-7.
ON-CAR SERVICE
PORT FUEL INJECTION COMPONENTS
CAUTION:
Before servicing an injector, fuel
rail, or pressure regulator,
it is
necessary to relieve the pressure in
the fuel system, to minimize the
risk of fire and personal injury.
(See "Fuel Pressure Relief
Procedure" below). To reduce the
chance of personal injury, cover
the fuel line with
a shop cloth to
collect the fuel, and then place the
cloth in an approved container.
FUEL PRESSURE RELIEF PROCEDURE
1. Connect fuel gage J 34730-1 or equivalent to fuel
pressure valve. Wrap a shop towel around fitting
while connecting gage to avoid spillage.
2. Install bleed hose into an approved container and
open valve to bleed system pressure.
Plenum
(Figure
C2-6)
Remove or Disconnect
1. Negative battery cable.
2. Throttle, 'F.V., and cruise control cable.
3. Cable retaining bracket.
4.
'I'hrottle body retaining bolts (4).
5. 'L'l'S and IAC valve electrical connectors.
6. Vacuum hoses.

6E3-C2-20 5.0L (VIN F) & 5.7L (WIN 8) DRIVEABILITY AND EMISSIONS
CONNECTOR - 441 BLUMlHT C5 IAC C0lL1'A" HI - 442 BLUIBLK C6 IAC COIL "A" LO - 443 GRNMlHT C4 IAC COIL "B" HI - 444 GRNIBLK C3 lAC COIL "B" LO v
START VALVE
CHART C-2C
IDLE AIR CONTROL (IAC) SYSTEM CHECK
S.OL (VIN F) & 5.7L (VIN 8) "F'" SERIES (PORT)
Circuit Description:
The ECM will control engine idle speed by moving the IAC valve to control air flow around the throttle
plates. It does this by sending voltage pulses to the proper motor winding for each IAC motor. This will cause
the motor shaft and valve to move
"IN" or "OUT" of the motor a given distance for each pulse received. ECM
pulses are referred to as "counts".
@ To increase idle speed - ECM will send enough counts to retract the IAC valve and allow more air to flow
through the idle air passage and bypass the throttle plates until idle speed reaches the proper rpm. This
will increase the ECM counts.
e To decrease idle speed - ECM will send enough counts to extend the IAC valve and reduce air flow through
the idle passage around the throttle plates. This will reduce the ECM counts.
Each time the engine is started and then the ignition is turned "OFF", the ECM will reset the IAC valve.
This is done by sending enough counts to seat the valve.
The fully seated valve is the ECM reference zero. A
given number of counts are then issued to open the valve, and normal ECM control of IAC will begin from this
point. The
number of counts are then calculated by the ECM. This is how the ECM knows what the motor
position is for a given idle speed.
The ECM uses the following information to control idle speed.
@ Battery voltage @ Engine speed @ Coolant temperature @ Throttle position sensor @ PIN switch e A/C clutch signal
Don't apply battery voltage across the IAC motor terminals. It will permanently damage the IAC motor
windin s. Test 6escription: Numbers below refer to circled
numbers on the diagnostic chart.
1. Continue with test, even if engine will not idle. If
idle is too low, "Scan" will display 80 or more
counts, or steps. If idle is high, it will display
"0"
counts.
Occasionally an erratic or unstable idle
[nay occur. Engine speed may vary 200 rpm or more up
and down. Disconnect IAC. If the condition is
unchanged, the IAC is not at fault.
There is a
system problem. Proceed to "Diagnostic Aids"
below.
2. When the engine was stopped, the IAC valve
retracted (more air) to
a fixed "Park" position for
increased air flow and idle speed during the next
engine start. A "Scan" will display 140 or more
coiints. 3. Be sure to disconnect the IAC valve prior to this
test.
The test light will confirm the ECM signals
by a steady or flashing light on all circuits.
4. There is a remote possibility that one of the
circuits is shorted to voltage which would have
been indicated by a steady light. Disconnect ECM
and turn the ignition "ON" and probe terminals to
check for this condition.
Diagnostic Aids:
Engine idle speed can be adversely affected by the
following:
@ ParMNeutral switch - If ECM thinks the car is
always in neutral, then idle will not be controlled
to the specified rpm when in drive range.
@ Leaking injector(s) will cause fuel imbalance and
poor idle quality due to excess fuel. See CHT.
A-7. @ Vacuum or crankcase leaks can affect idle. @ Whenthethrottleshaftorthrottlepositionsensor
is binding or sticking in an open throttle position,
the ECM does not know if the vehicle has stopped
and does not control idle.
@ Check A.I.R. management s stem for intermittent
air to orts while in "~losed~oo~". @ In ad&tion to electrical control of EGR, be sure to
examine the EGR valve for proper seating.
@ Faulty battery cables can result in voltage
variations. The ECM will try to compensate,
which results in erratic idle speeds.
@ 'I'he ECM will com ensate for A/C com ressor
clutch loacls. [.ass ofthe NC request sign8 would
he 11lost apparent, in neutral. @ Contalninatecl fuel can adverse1 affect idle. @ Perform i~!jector balance test C~ART C-2A. If ,111 OK, refer to "Rough, Unstable, Incorrect Idle or St ,tllinqW SJ tnptcfinsiin S~'ction "11''.