Engine Idle Speed Control Operation

The engine idle speed is controlled by the Powertrain Control Module (PCM) through the Idle Air Control (IAC) valve. There are several reasons for idle speed control:
1. Maintain the engine idle speed at the specified RPM at all times. The engine idle speed can vary due to any of the following reasons:
^ A change in the load applied to engine (when an electrical load is applied, the automatic transaxle is shifted to R, D, 2 or L ranges, the A/C is turned ON, the headlights or stop lights are turned ON, etc.).
^ A change in the atmospheric pressure.
^ A change in the engine's condition over time.
2. Improve the starting performance of the engine.
3. Improve the driveability of the engine during warm up.
4. Compensate for the change in the air/fuel mixture ratio when decelerating (dash-pot effect).