Idle Speed/Throttle Actuator - Electronic: Description and Operation

The purpose of the Idle Air Control (IAC) valve is to control the engine idle speed while preventing stalls due to changes in the engine load. The IAC valve, mounted in the throttle body, controls the bypass air around the throttle plate. By moving a conical valve known as a pintle in to decrease air flow or out to increase air flow, a controlled amount of air can move around the throttle plate. If the engine RPM is too low, the PCM will retract the IAC pintle, resulting in more air being bypassed around the throttle plate. If the engine RPM is too high, the PCM will extend the IAC pintle, allowing less air to be bypassed around the throttle plate.

The IAC pintle moves in small steps called counts. During idle, the proper position of the IAC pintle is calculated by the PCM based on the battery voltage, the coolant temperature, the engine load, and the engine RPM. If the RPM drops below a specified value, and the throttle plate is closed, the TP sensor voltage is between 0.20-0.74, and the PCM senses a near stall condition. The PCM will then calculate a new IAC pintle position in order to prevent stalls. If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be incorrect. In this case, the IAC has to be reset.

The IAC resets when the key is cycled on and then off.

When servicing the IAC, the sensor should only be disconnected or connected with the ignition off in order to prevent having to reset the IAC.

The position of the IAC pintle affects engine start up and the idle characteristics of the vehicle. If the IAC pintle is open fully, too much air will be allowed into the manifold. This results in high idle speed, along with difficult starting and a lean air/fuel ratio. DTC P0507 may set. If the IAC pintle is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed, along with difficult starting and a rich air/fuel ratio. DTC P0506 may set. If the IAC pintle is stuck part way open, the idle may be high or low and will not respond to changes in engine load.