Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Air Control (IAC) Valve Assembly:

PURPOSE
The purpose of the Idle Air Control (IAC) valve assembly is to supply metered air to the engine when the throttle is closed. The Electronic Control Module (ECM) controls the IAC valve to insure good idle quality at all temperatures and engine loads.

Idle Air Control (IAC) Valve Air Flow Diagram:

OPERATION
The IAC valve, mounted in the throttle body, controls bypass air around the throttle valve. By moving a conical valve known as a pintle, IN toward the seat (to decrease air flow), or OUT away from the seat (to increase air flow), a controlled amount of air moves around the throttle valve. If rpm is too low, more air is bypassed around the throttle valve to increase it. if rpm is too high, less air is bypassed around the throttle valve to decrease it.

During idle, the proper position of the IAC valve is calculated by the ECM, based on battery voltage, coolant temperature, engine load, and engine rpm. If the rpm drops below specification and the throttle valve is closed, the ECM senses a near stall condition and calculates a new valve position to prevent stalling.