Idle Air Control - Vehicles Without 4L80-E Transmission: Description
WARNING: This page does not describe the selected car, but rather 35 other vehicles, including the 1992 Pontiac Trans Sport, 1992 Oldsmobile Silhouette, 1992 Oldsmobile Bravada, 1992 GMC Yukon, and 1992 GMC Vandura Special. However, it is still accessible from the selected car via links, so may be relevant.
The ECM controls engine idle speed with the IAC valve. To increase idle speed, the ECM retracts the IAC valve pintle away from its seat, allowing more air to pass by the throttle bore. To decrease idle speed, it extends the IAC valve pintle towards it's seat, reducing bypass air flow. A Tech 1 "Scan" tool will read the ECM commands to the IAC valve in counts. Higher counts indicate more air bypass (higher idle). Lower counts indicate less air is allowed to bypass (lower idle).