Engine Idle Speed Control

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.