Idle Air Control (IAC) Valve - It Manages Your Engine's Idle Speed
Idle Air Control (IAC) Valve – It Manages Your Engine’s Idle Speed

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


Idle Air Control (IAC) Valve – It Manages Your Engine’s Idle Speed

So, An idle air control valve (IAC), controls the engine’s idle speed.

The (IAC) is controlled electrically; which gets its input from the vehicle’s (ECU). The (IAC) either bypasses the throttle or operates the throttle butterfly valve directly. The actuator consists of a linear servo actuator servo motor; that controls a plunger, which varies air flow through the throttle body. Consequently, the position of the servomotor is controlled digitally, by the engine (ECU). This allows the idle speed to be constant. The linear servo is most commonly; a combination of a DC motor, lead screw and a digital optical encoder.

There is essentially no difference in efficiency between the technique of; bypassing the throttle butterfly and operating the butterfly itself. As a result, the (IAC) allows the (ECU) to maintain minimum (RPM); irrespective of changes in engine load.

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

The result is an engine that fails to maintain idle (RPM) and frequently 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 elevated idle (RPM). Tip: If the engine speed is too high; too low, or stalling, the problem may not be the idle speed control system; but an engine vacuum leak. So, check for vacuum leaks first, to rule out this possibility.

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

Thank You !