Idle Air Control Valve

The IAC valve controls engine idle speed, while preventing stalls due to changes in engine load. The IAC valve is mounted on the throttle body, and controls by-pass air around the throttle plate. By moving a conical valve inward (to decrease air flow), or outward (to increase air flow), a controlled amount of air can move around the throttle plate.

If RPM is too low, more air is bypassed to increase RPM. If RPM is too high, less air is bypassed to decrease RPM. During idle, the ECM determines the correct position of the IAC valve based on battery voltage, coolant temperature, engine load and RPM. IAC valve affects only the idle characteristics of the vehicle.