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Idle Air Stabilizer Valve

The idle air stabilizer valve operates continuously when the ignition is on and the coolant temperature sensor is connected. To check that the valve is functioning, start the engine. The valve should vibrate and hum slightly. If the valve is not operating, check that the idle switch on the throttle valve is closed and functioning correctly as described below. If no faults are found with the idle switch, turn the engine off, disconnect the harness connector from the valve, and check for continuity at the terminals on the valve. If there is no continuity, the valve is faulty and should be replaced.

To check the idle stabilization function of the control unit, measure the current flow to the valve. Fig. 7-11 shows a special wire harness used to hook up an ammeter (0 to 1000 mA range). Alternately, a harness can be fabricated to allow hook-up of an ammeter as shown.


Disconnecting the idle stabilizer valve's harness connector while the engine is running will damage the electronic control unit.

Connecting the test harness to a meter set on the voltage scale will damage the electronic control unit.

Start the engine and briefly raise the engine speed to over 2100 rpm, then let the engine return to idle. Repeat this step four times to clear the control unit's hot-start fast idle function. With the engine running, the idle stabilizer current reading should fluctuate between 390 and 450 mA. Disconnect the harness connector from the coolant temperature sensor. The current reading should be steady at approximately 430 mA.


The small female terminals in the differential pressure regulator harness connector are easily damaged. If fabricating a test harness, use the appropriate male terminals (Volkswagen part no. N 17 457 2) to make connections with the harness connector.

Fig. 7-11. Test harness Volkswagen special tool no. VW 1315 A/2 (order no. TV1 315 OA2 025 ZEL) being used to connect ammeter and measure idle air stabilizer current from control unit.


Idle air stabilizer current depends on idle speed. It will normally fluctuate between 400 and 1100 mA to correct idle speed if the engine is too cold, if the coolant temperature sensor is faulty, if idle speed is incorrectly adjusted, if there is an engine vacuum leak, or when electrical accessories are running.

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