Express 1/2 Ton Van V8-5.7L VIN R (1999)
Idle Air Control Motor (IAC): Description and Operation
The diagnosis of Idle Air Control (IAC) can be found in Idle Air Control System Diagnosis.
If the IAC valve is disconnected or connected when 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 speed 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.
