The idle air control (IAC) valve, is located on the throttle body, of fuel injected engines.

Here, it works with the vehicle’s (ECU) to, electrically regulate airflow to the engine, ensuring smooth idling.

The (IAC) valve, controls the air needed, to maintain a steady idle speed. It essentially acts, as a bypass of the throttle body plate.

The idle air control (IAC) valve is controlled electrically. And, gets its input from, the vehicle’s (ECU). The (IAC) either, bypasses the throttle or operates, the throttle butterfly valve directly. Consequently, computer controls and electronic fuel injection, made efficient and responsive idle control easier to achieve.

Motorized or electronic (IAC) valves can open or close the bypass. Usually, by varying degrees, depending on the engine load. For example, with no loads, the idle air control (IAC) valve might open, only a little. During parking maneuvers, power steering or electrical load, slows the engine down. Then, the (IAC) valve, opens a bit more, to provide consistent engine speed and enough power, to prevent stalling.

So, the most common failure, is partial or complete jamming of the actuator.

The result is an engine that fails to maintain idle (RPM) and often stalls. A jammed actuator may be freed, simply by cleaning it. However, an actuator that has stopped working, due to a fault in its servo motor, will need replacement. Air leaks in either the stepper housing or pipes, will cause high idle (RPM).

Tip: If the engine speed is too high, too low, or stalling. Then, the problem may not be, the idle speed control system. But, could actually be, an engine vacuum leak. So, check for vacuum leaks first, to rule out this possibility.

Note: The new idle air control (IAC) valve, may or may not come, with a new seal. So, remember to replace the seal, any time a sealed part, is removed from the engine. Above all, to avoid a vacuum or coolant leak, where coolant runs through the (IAC) valve body.

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Idle Air Control Valve (IAC) – Function – Failure Symptoms – Testing

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