1989 Audi 80 Base, AutomaticFACTORY OEM SERVICE PROCEDURE

Idle Speed Stabilization System

  1. Ensure engine temperature is below 68°F (20°C). Disconnect harness connector at the thermoswitch. Check for continuity to ground.
  2. If no continuity, replace thermoswitch. If continuity is present, warm thermoswitch to at least 104°F (40°C). Thermoswitch should now show an open circuit. If not, replace thermoswitch.
  3. Warm engine to 176°F (80°C) minimum. Disconnect electrical harness for idle stabilizer valve. Connect a voltmeter across both terminals. Turn ignition on. Battery voltage should be present.
  4. If battery voltage is present, reconnect idle stabilizer valve. Touch idle stabilizer valve and check for vibrations. If not felt, replace idle stabilizer valve.
  5. If no voltage present in step 3), remove idle stabilizer control unit (located in relay panel). Turn ignition on and check for 12 volts between terminals No. 14 (socket 11) and 5 (socket 12).
  6. If no voltage present, repair wiring. Turn A/C on, and check for 12 volts between terminal No. 2 (socket 12) and 5 (socket 12). If no voltage, check wiring from A/C relay pin No. 87M.
  7. Check resistance between terminals No. 4 (socket 12) and 11 (socket 11). Ohmmeter should indicate 20-40 ohms. If not, check continuity of wiring between idle stabilizer valve and relay board.
  8. Ensure throttle switch is at idle position. Check for 12 volts at terminal No. 8 (Gray wire). If voltage is not present, check and adjust throttle switch or repair wiring. With voltage present at idle, slightly open throttle. Ensure voltage drops to zero.
  9. Disconnect thermoswitch harness lead. Check for continuity between terminal No. 13 (socket 11) and thermoswitch lead (Blue/Green wire). If no continuity, repair wiring. If all circuits of idle stabilizer system are okay and idle stabilizer valve still does not work, replace idle stabilizer control module.


  1. Ensure engine temperature is below 68°F (20°C). Disconnect harness connector at the thermoswitch. Check for continuity to ground.
  2. If no continuity, replace thermoswitch. If continuity is present, warm thermoswitch to at least 104°F (40°C). Thermoswitch should now show an open circuit. If not, replace thermoswitch.
  3. Warm engine to 176°F (80°C) minimum. Disconnect electrical harness for idle stabilizer valve. Connect a voltmeter across both terminals. Turn ignition on. Battery voltage should be present.
  4. If battery voltage is present, reconnect idle stabilizer valve. Touch idle stabilizer valve and check for vibrations. If not felt, replace idle stabilizer valve.
  5. If no voltage present in step 3), remove idle stabilizer control unit (located in relay panel). Turn ignition on and check for 12 volts between terminals No. 14 (socket 11) and 5 (socket 12).
  6. If no voltage present, repair wiring. Turn A/C on, and check for 12 volts between terminal No. 2 (socket 12) and 5 (socket 12). If no voltage, check wiring from A/C relay pin No. 87M.
  7. Check resistance between terminals No. 4 (socket 12) and 11 (socket 11). Ohmmeter should indicate 20-40 ohms. If not, check continuity of wiring between idle stabilizer valve and relay board.
  8. Ensure throttle switch is at idle position. Check for 12 volts at terminal No. 8 (Gray wire). If voltage is not present, check and adjust throttle switch or repair wiring. With voltage present at idle, slightly open throttle. Ensure voltage drops to zero.
  9. Disconnect thermoswitch harness lead. Check for continuity between terminal No. 13 (socket 11) and thermoswitch lead (Blue/Green wire). If no continuity, repair wiring. If all circuits of idle stabilizer system are okay and idle stabilizer valve still does not work, replace idle stabilizer control module.
Chapter Navigation
Return to Chapter: Cis Digital Control
Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.

Shop Manual-Ready ToolsCompare Repair QuoteQuote Shield Pro

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.