S10/T10 P/U 2WD V6-262 4.3L VIN Z TBI (1995)
Idle Air Control (IAC) Valve: Testing and Inspection
Idle Air Control (IAC) Reset Procedure
With Powertrain Control Module (PCM)
Idle Air Control (IAC) System
The diagnosis of idle Air Control (IAC) can be found in Idle Air Control (IAC) Valve. Refer to C Charts. Under Computer and
Controls/System Diagnosis/Procedures. See: Computers and Control Systems/Testing and Inspection
If the IAC valve is disconnected or connected with the engine running, the idle RPM may be wrong. The IAC valve may be reset by disconnecting
negative battery terminal for 10 seconds then reconnect battery cable, turn ignition "ON," engine "OFF" for 5 seconds then turn ignition "OFF" for
10 seconds.
The IAC valve affects the idle characteristics of the engine. If it is open fully, too much air will be allowed in 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.
^
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 Diagnostic Trouble Code (DTC) 44. Scan tool or voltmeter will read an oxygen sensor output less than 300 mV (0.3 volt).
Check for low regulated fuel pressure or water in fuel. A lean exhaust with an Oxygen Sensor (O2S) output fixed above 800 mV (0.8 volt) will
be a contaminated sensor, usually silicone. This may also set a DTC 45.
^
System too rich (low air/fuel ratio) - Idle speed too low. Scan counts usually above 80. System obviously rich and may exhibit black exhaust
smoke. Scan tool and/or voltmeter will read an Oxygen Sensor (02S) signal fixed above 800 mV (0.8 volt).
With Vehicle Control Module (VCM)
IAC RESET
The diagnosis of Idle Air Control (IAC) refer to C Charts. Under Computer and Controls/System Diagnosis/Procedures. See: Computers and
Control Systems/Testing and Inspection
If the IAC valve is disconnected or connected while the engine is running, the idle RPM may be wrong. The IAC valve may be reset by turning the
ignition switch "ON" for 10 seconds, "OFF" for 5 seconds.
The IAC valve affects the idle characteristics of the engine as well as throttle follow-up to compensation for sudden throttle closing. If it is open
fully too much air will be allowed in 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.
SYMPTOMS
When there is a problem with idle air control system or refer to Idle Air Control (IAC) Check. Refer to C Charts. Under Computer and
Controls/System Diagnosis/Procedures.
^
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 DTC P0171.
Scan tool and/or voltmeter will indicate an oxygen sensor output less than 300 mV (0.3 volt). Check for low regulated fuel pressure or water in
fuel. A lean exhaust with an Oxygen Sensor (O2S) output fixed above 800 mV (0.8 volt) may be the result of a contaminated sensor, usually
silicone. This may also set a DTC P0172. Refer to Diagnostic Trouble Code Charts. Under Computer and Controls/System
