What does it mean?
Idle air control does just as its name suggests and controls the idle by allowing a certain amount of air to enter the engine. This keeps the idle at a specific RPM, and helps the engine to run better, and last longer. When the throttle body is closed, a very small amount of ambient air can get by the throttle plate. This gives the idle control to the IAC, which is a device that uses a plunger to monitor the amount of air that goes into the engine. Air is controlled by feedback circuits that control the IAC and only allow the amount of air that is necessary. As the plunger moves it allows for either more air or less air as per the needs of the engine determined by the ECU.