Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Air Control Valve Assembly (IAC):

The purpose of the IAC valve is to control the engine idle speed and prevent stalling due to changes in engine load. The IAC valve, mounted in the throttle body, controls the amount of air bypassed around the throttle plate. This is actually a controlled vacuum leak. If more air is bypassed, idle speed will increase, and if less air is bypassed, the idle speed will decrease. The IAC valve accomplishes this by moving a conical shaped pintle in, to decrease bypassed air and out, to increase bypassed air. The ECM uses sensor and switch inputs to control the position of the IAC pintle. If the pintle is stuck open, the idle speed will remain high. If the pintle is stuck closed, the idle speed will be too low, and stalling may occur. If the pintle is stuck partially open, the idle speed will be higher than normal, and there will be no response to changes in engine load such as A/C ("ON") or transmission in ("Drive").