Pontiac Fiero 1988 Service Manual page 501

6 E 2 - A - 4 S
DRIVEABILITY
A M D EMISSIONS
- FUEL INJECTION (TB1J
AIR
FLOW
5-30-87
ECM
IAC COIL "A" HI
LT BLU/WHT 441 —
W7
IAC COIL "A" HI
LT BLU/BLK 442
—
W%7
IAC COIL "A"
1 0
LT GRN/WHT 443 —
W§
IAC COIL " B " HI
LT GRN/BLK 4 4 4 —
WB
IAC COSL " 1 " LO
*7S3209-6E
4-6-87
CODE 35
IDLE S P E E D ERROR
2.5L
f f
P
f f
SERIES (TBI)
Circuit Description: • • - •• •
;
. . . -. . . -
:
Code 35 will set, when the closed
throttle
engine speed is 150 rpm above or below the desired idle speed for
20 seconds. Review general description in Section "C".
Test Description:
Numbers below refer to circled
numbers on the diagnostic chart.
1. Continue with test, even if engine will not idle. If
the idle is too low, "Scan" will display 80 or more
counts, or steps. If idle is too high, it will display
"0" counts. Occasionally, an erratic or unstable
idle may 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.
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 100 or more
counts.
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:
A slow unstable idle may be caused by a system
problem that cannot be overcome by the IAC. "Scan"
counts will be above 60 counts, if idle is too low, and
"0" counts, if idle is too high.
If idle is too high, stop engine. Ignition "ON".
Ground diagnostic terminal. Wait 45 seconds for
IAC to seat, then, disconnect IAC. Start engine. If
idle speed is above 800 rpm, locate and correct vacuum
leak.
System too lean (High Air/Fuel Ratio)
Idle speed may be too high or too low. Engine
speed may vary up and down, disconnecting IAC
does not help. May set Code 44.
"Scan" and/or Voltmeter will read an oxygen
sensor output less than 300 mv (.3 volts). Check
for low regulated fuel pressure or water in fuel. A
lean exhaust, with an oxygen sensor output fixed
above 800 mv (.8 volts), will be a contaminated
sensor, usually silicone. This may also set a Code
45. ;' - ; - • • • • \ '
System too rich (Low Air/Fuel Ratio)
Idle speed too low. "Scan" counts usually above
80. System obviously rich and may exhibit black
smoke exhaust.
"Scan" tool and/or Voltmeter will read an oxygen
sensor signal fixed above 800 mv (.8 volts).
Check: , • • :
High fuel pressure
Injector leaking or sticking
Throttle Body - Remove IAC and inspect bore for
foreign material or evidence of IAC valve
dragging the bore.
IAC Harness connections
Carefully inspect harness connections for proper
contact.
PCV Valve
An incorrect or faulty PCV Valve may result in an
incorrect idle speed.
Refer to "Rough, Unstable, Incorrect Idle or
Stalling" in Symptoms in Section "B".