GM Cadillac Deville_Fleetwood_ELD_Seville 1990-1998

Idle Speed Adjustment


The Idle Air Control (IAC) valve assembly controls engine idle speed. 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 solenoid responds by positioning the IAC valve to control the amount of bypassed air. By varying the amount of air intake, different idle speeds can be achieved. When the pintle is in, the valve is closed and a low idle speed results. When the pintle is out, the valve is open and high idle speeds occur. The PCM monitors engine rpm and increases or decreases the IAC duty cycle in order to achieve the desired rpm. There are no external mechanical adjustments to be made.

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