Circuit Description

This test determines if idle control system is maintaining the proper idle speed. The IAC system controls idle speed by allowing a certain amount of air to bypass the throttle body (throttle plate closed during idle) through the IAC valve. The PCM controlled IAC motor moves a pintle in and out of IAC valve, varying the amount of air entering the intake manifold.

If engine idle speed is greater than the desired idle speed and all test conditions are met, the PCM will cycle the IAC valve and expect to see a change in the MAF sensor reading. If no change occurs DTC P1509 will set. If a change occurs indicating the IAC is responding, then DTC P0507 will set.