Operation CHARM: Car repair manuals for everyone.

Idle Speed/Throttle Actuator - Electronic: Description and Operation

Figure 4C-2 - IAC Air Flow Diagram:




Idle Air Control Valve Assembly
The purpose of the Idle Air Control (IAC) valve assembly is to control engine idle speed while preventing stalls due to changes in engine load.
The IAC valve is mounted in the upper manifold assembly and controls bypass air around the throttle valve by moving a conical valve known as a pintle. By moving the pintle in (toward the seat to decrease air flow), or out (away from the seat to increase air flow), a controlled amount of air is bypassed around the closed throttle valve. If idle speed is too low, more air is bypassed around the throttle valve to increase RPM. If idle speed is too high, less air is bypassed around the throttle valve to decrease RPM.
The PCM moves the IAC valve in small steps called counts. These can be measured by a scan tool which plugs into the Data Link Connector (DLC).
During idle, the proper position of the IAC valve is calculated by the PCM, based on battery voltage, Engine coolant temperature, engine load, and engine RPM. If the RPM drops below specification and the throttle valve is closed, the PCM senses a near stall condition and calculates a new valve position to prevent stalling.

If the IAC valve is disconnected and reconnected while the engine is running, the resulting idle speed may be wrong and resetting of the IAC valve will be required.
After running the engine, the AC valve will reset when the ignition is turned "OFF." When servicing the IAC valve, it should only be disconnected or connected with the ignition "OFF."