Discovery I (LJ) V8-3.9L (1994)
Idle Air Control Valve: Description and Operation
Idle Air Control Valve
PURPOSE AND OPERATION
At idle, a bypass port allows a measured amount of air to enter the plenum chamber when the following conditions are present:
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Road speed less than 3 mph
^
Throttle closed
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Engine above 50 rpm
The size of the air orifice is controlled by the Idle Air Control Valve (IACV). This is a stepper motor mounted in the by-pass port that can provide
a variable restriction of bypass air flow. Stepper motor position is controlled by the Engine Control Module (ECM).
The ECM makes idle air control adjustments based on sensor inputs (ambient temperature, engine load produced by accessories such as air
conditioning or defrosters) to keep idle speed sufficient for the situation.
Failure of the stepper motor can result in either a high or low idle speed, engine stall or no-start.
Resistance in the IACV coils ranges from 40-60 ohms at room temperature and up to 70 ohms when hot.