Camaro V8-350 5.7L (1989)
Idle Speed/Throttle Actuator - Electronic: Description and Operation
Idle Air Control (IAC) Valve Assembly
IAC Valve Air Flow
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The purpose of the idle air control (IAC) valve is to provide a way for the ECM to control engine idle speed. The IAC valve works by controlling
the amount of air that bypasses the throttle plate.
By moving a conical shaped valve, known as a pintle, towards its seat, the IAC valve reduces the bypass air rate which in turn causes engine speed
to be reduced. Conversely, by moving the pintle away from its seat, The IAC valve increases the bypass air rate and increases the engine speed. If
the ECM detects that the idle speed is not correct, it will command the IAC valve to bypass more or less air to regulate idle speed.
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The ECM 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.
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If the IAC valve is disconnected and reconnected with the engine running, the idle rpm may be wrong. In this case, the IAC has to be reset.
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When servicing the IAC, it should only be disconnected or connected with the ignition OFF. This will keep from having to reset the IAC.
^ For diagnosis and testing procedures, see COMPUTERIZED ENGINE CONTROLS.
