20V Motronic ECU System

1991 200TQ and 1992-95 S4/S6 with 20V Turbo Engine:

Idle Stabilizer Valve (ISV), or Idle Air Control (IAC) valve

The idle stabilizer valve or what is also called the Idle Air Control valve is a rotary valve that allows air to bypass the throttle valve and raise or lower the idle speed of the engine. See the photos below for specific location details


1991 200TQ 20V


1992-95 S4/S6 Idle Air Control (IAC) Valve

The idle speed is raised during the warm up period of the engine and the idle speed is maintained depending on changes in load. Increased load from the alternator when the lights are turned on, and increased load from the A/C compressor cycling will change the amount the idle stabilizer valve is opened.

The rotary valve is cycled with a DC voltage which will cause the motor armature to work against a return spring. The duty cycle of this DC voltage determines the position of the rotary valve and the amount of the opening to allow air to pass through [1].

The idle stabilizer valve can also stick from oil/crude built up inside and this can cause idle problems. Removing the ISV and cleaning it with carb cleaner may help.

To clean the ISV or IAC, you can remove the valve from the engine hoses and leave the electrical connector plugged in, then run the ECU Output tests to cycle the valve open and closed while you spray some carburetor cleaner in the valve openings.

Audi parts on-line catalog

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References: [1] Audi of America, Technical service training publication:

"The New 20V Turbo Engine for the Audi 200 Quattro-publication All rights reserved.

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