Idle Air Control (IAC) Valve (Applications Without ETC)
WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2005 Mercury Sable, 2005 Mercury Mountaineer, 2005 Mercury Monterey, 2005 Mercury Montego, and 2005 Mercury Mariner. However, it is still accessible from the selected car via links, so may be relevant.
The IAC valve assembly controls the engine idle speed and provides a dashpot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the IAC valve to control the amount of bypassed air. The PCM monitors engine RPM and increases or decreases the IAC duty cycle in order to achieve the desired RPM.
NOTE:
The IAC valve assembly is NOT ADJUSTABLE and CANNOT BE CLEANED, also some IAC valves are normally open and others are normally closed. Some IAC valves require engine vacuum to operate.
The PCM uses the IAC valve assembly to control:
- No touch start.
- Cold engine fast idle for rapid warm-up.
- Idle (corrects for engine load).
- Stumble or stalling on deceleration (provides a dashpot function).
- Over-temperature idle boost.