Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1994 Audi 90 CS QuattroFACTORY OEM SERVICE PROCEDURE
Idle Air Control (IAC) Valve
- Disconnect electrical connector from Idle Air Control (IAC) valve. See ELECTRICAL COMPONENT LOCATIONS table at beginning of article. Measure resistance between IAC valve connector terminals. If resistance is not 7-11 ohms, replace IAC valve. If resistance is 7-11 ohms, remove IAC valve.
- Looking through hole in IAC valve, check for scored rotary slide valve. Replace IAC valve if rotary slide valve is scored. If rotary slide valve is okay, reconnect IAC valve connector. Turn ignition on. Initiate Output DTM. See OUTPUT DTM in G - TESTS W/ CODES article in the ENGINE PERFORMANCE Section. Observe rotary slide valve when IAC valve is activated during Output DTM.
- If rotary slide valve travels freely from stop to stop, system is okay. If rotary slide valve shows signs of movement but does not travel freely from stop to stop, replace IAC valve. If rotary slide valve is not activated during Output DTM, check wiring. If wiring is okay, replace ECM.
Factory Service Tools
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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.