Express 1/2 Ton Van V8-5.7L VIN R (1999)
Circuit Description
The Control Module (PCM/VCM) controls idle speed with an Idle Air Control (IAC) valve. The Desired RPM is based on sensor inputs and the actual
engine RPM. Four circuits are used to control the IAC valve, allowing a precise amount of air into the intake manifold. In order to increase the idle
RPM, the Control Module will command the valve pintle to move away from its seat allowing more air to bypass the throttle plate. To decrease RPM the
Control Module commands the IAC pintle to move closer to its seat causing a lower airflow to bypass the throttle plate. A scan tool will display the
Control Module commands to the IAC valve in counts. The higher the counts, the more air is allowed to bypass the throttle plate. Lower counts indicates
less air is commanded by the Control Module.
IAC Valve Reset Procedure Without A Scan Tool
1. Turn ON the ignition leaving the engine OFF for 5 seconds.
2. Turn OFF the ignition for 10 seconds.
3. Start the engine and check for proper operation.
IAC Valve Reset Procedure With Scan Tool
1. Turn ON the ignition leaving the engine OFF.
2. Install a scan tool.
3. Select F4 Misc. Tests.
4. Select F3 IAC System.
