Idle Air Control (IAC) Valve

Idle Air Control (IAC) Valve

The IAC valve is located on the inlet manifold and is secured with four Torx head screws. The IAC valve comprises a stepper motor and a pintle valve enclosed in a plastic housing. The IAC valve is directly controlled by the ECM.

The IAC valve opens or closes the pintle valve which is situated in an air passage in the throttle housing, allowing air to bypass the throttle disk and flow straight into the inlet manifold. By changing the amount the IAC valve is open, the ECM can control engine idle speed and cold start air flow requirements by adjusting the flow of air through the passage. The position of the IAC valve can be checked using Testbook. When adjusting to the displayed limits, it is important that no electrical or mechanical loads are applied (cooling fan, A/C etc.).

During cold starting, the ECM indexes the IAC valve to open a calculated amount to provide a level of fast idle, dependent on engine coolant temperature. As the engine warms, the fast idle is decreased by gradually closing the IAC valve pintle until normal operating temperature is reached.

The position of the IAC valve can be checked using TestBook and should be within the range of 20 to 40 steps when the engine is running at normal operating temperature. If it is identified as being outside this range it can be adjusted to within range using TestBook. This ensures that the IAC valve is at the optimum position within its range for providing further movement to compensate for changes in engine load or temperature in accordance with signals from the ECM.

If the IAC valve fails, the engine may continue to idle depending on the position of the stepper motor prior to failure.