Pontiac Fiero 1988 Service Manual page 631

6E3-A-48 DRIVABILITY AND EMISSIONS - FUEL INJECTION (PORT)
A [ R
THROTTLE
FLOW BODY
IAC
CONNECTOR
ECM
441 BLU7WHT
442 BLU/BLK
443 GRN/WHT
• 444 GRN/BLK
C5
C6
TO COLD START VALVE
AIR INLET
IAC COIL " A " HI
IAC COIL " A " LO
IAC COIL " B " HI
IAC COIL " B " LO
5-19-87
2-18-87
5S1800-6E
CODE 35
IDLE SPEED ERROR
2.8L " P " SERIES (PORT)
Circuit Description:
Code 35 will set when the closed throttle engine speed is 75 rpm above or below the correct idle speed for
45 seconds. Review general discription in Section "C". Following are nominal warm engine idle speeds:
AUTO MANUAL ALDL
Neutral 900 ± 75 900 ± 75 1000 + 75
Drive 800 ± 75 1000 ±75
Test Description:
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 "O"
counts and may be caused by a vacuum leak.
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 during the next engine start. A
"Scan" will display 95 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 CKTs 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 corrected by the IAC. "Scan"
counts will be above 60 counts if too low and "0" counts
if too high.
If idle is too high, stop engine. Ignition "ON"
Ground diagnostic terminal. Wait a few seconds for
IAC to seat then disconnect IAC. Start engine. If idle
speed is above 800 ± 5 0 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, and disconnecting
IAC does not help. This may set Code 44.
"Scan" and/or voltmeter will read an oxygen
sensor output less than 300 mV
(.3V).
Check for
low regulated fuel pressure or water in fuel. A
lean exhaust with an oxygen sensor output fixed
above 800 mV (.8 mV) 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 (.8V).
Check:
High fuel pressure
Injector leaking or sticking
Map sensor Ignition "ON", engine stopped.
Compare MAP signal voltage with a known good
vehicle with the same sensor. Voltage should be
the same, ± 400 mV
(.4V).
Also, disconnect MAP
Sensor electrical connector. If idle improves,
substitute a known good sensor and recheck.
Throttle body Remove IAC and inspect bore for
foreign material or evidence of IAC valve
dragging the bore.
A/C compressor or relay failure See CHART C-10.
Refer to "Rough, Unstable, Incorrect Idle or
Stalling" in Symptoms in Section "B".