Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Air Control Valve:

Throttle Body (Exploded View):

IAC Valve Air Flow:

DESCRIPTION
The Idle Air Control Valve (IAC) valve allows the PCM to maintain correct idle speed under different operating conditions. The valve consists of a stepper motor that moves a valve pintle in and out of its bore. The position of the pintle is measured in "COUNTS". The more counts, the farther open the valve is, and the more air is bypassed around the throttle valve.

OPERATION
The IAC controls the amount of air bypassed around the throttle plate. When more air is bypassed, idle speed increases, when less air is bypassed, the idle speed decreases. The IAC valve accomplishes this by moving a conical shaped pintle "IN" to decrease bypassed air and "OUT" to increase bypassed air. This can be seen as counts displayed on a "Scan" tool. Inward Movement of the pintle = Decreased RPM = Lower Counts. Outward Movement of the pintle = Increased RPM = Higher Counts.

The PCM monitors battery voltage, coolant temperature, engine rpm, vehicle speed, throttle position and auxiliary engine loads in determining what commands to send the IAC valve. The IAC valve moves by taking a series of steps known as "COUNTS". The higher the number of counts, the farther the pintle is moved from its seat and more air is bypassed.

If the IAC valve is disconnected and reconnected with the engine running, the idle rpm may be wrong. In this case, the PCM needs to re-learn the IAC position (IAC reset).

When servicing the IAC, it should only be disconnected or connected with the ignition OFF. This will keep from having to reset the IAC. If the IAC valve needs to be reset, depress the accelerator slightly and start the engine. Hold the throttle steady while the engine runs for about 5 - 10 seconds, then turn engine "OFF" for 10 seconds. IAC valve position should be reset.



Location:
The IAC valve is mounted to the throttle body.