Idle Speed/Throttle Actuator - Electronic: Description and Operation

IDLE AIR CONTROL (IAC) VALVE
The purpose of the Idle Air Control (IAC) valve is to control engine idle speed, while preventing stalls due to changes in engine load. The IAC valve, mounted in the throttle body, controls 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 RPM is too low, the PCM retracts the IAC pintle, resulting in more air being bypassed around the throttle plate to increase RPM. If RPM is too high, the PCM extends the IAC pintle, allowing less air to be bypassed around the throttle plate, and decreasing RPM.

The IAC pintle moves in small steps called counts. During idle, the proper position of the IAC pintle is calculated by the PCM based upon 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 (TP sensor voltage is between 0.20-0.74), the PCM senses a near stall condition. The PCM then calculates 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 wrong. In this case, the IAC has to be reset.

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

The IAC should only be disconnected or connected with the ignition off in order to avoid having to reset the IAC.

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