Idle Air Control (IAC) Valve Assembly
WARNING: This page is about a different car, the 1995 Ford Windstar. However, it is still accessible from the selected car via links, so may be relevant.
IAC valve assembly is used to control idle speed and provide a dashpot function. IAC valve assembly meters inlet air around the throttle plate through a by-pass within the IAC valve assembly and throttle body. See Fig 1 .
The PCM determines desired idle speed or air by-pass, and signals the IAC valve assembly through specified duty cycle. The IAC solenoid is built in IAC valve assembly. IAC solenoid responds by positioning the IAC valve to control amount of air by-passed. PCM monitors engine speed and adjusts IAC duty cycle to achieve desired RPM.