Idle Speed: Description and Operation

The Powertrain Control Module (PCM) controls the engine idle speed by adjusting the position of the Idle Air Control (IAC) motor pintle. The IAC is a bi-directional motor driven by 2 coils. The PCM pulses current to the IAC coils in steps, or counts, to extend the IAC pintle into a passage in the throttle body and decrease air flow. The PCM reverses the current pulses to retract the pintle and increase the air flow This method allows highly accurate control of the idle speed and a quick response to changes in the engine load.