Engine Idle Speed Control

WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

The engine idle speed is controlled by the PCM through the idle air control (IAC) valve. There are several reasons for idle speed control:

In order to 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 such as when the rear defogger is operating, 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.
In order to improve the starting performance of the engine.
In order to improve the driveability of the engine during warm up.
In order to compensate for the change in the air/fuel mixture ratio when decelerating.