Audi S3 Starting Issues Point to Faulty Cam Sensor

Based on my experience with a 2002 Audi S4, I dealt with nearly identical symptoms. As someone with moderate automotive repair experience, I initially thought it was just a simple sensor issue. The engine misfire symptoms started gradually, difficult starts, unusual stalling at idle, and eventually the check engine light came on. After proper sensor testing at the workshop, they discovered the encoder wheel on both camshafts was defective, causing incorrect ignition timing and engine control issues. The total repair came to 695 Euro, including parts and labor. The fix resolved all issues, no more car stalling, smooth idle, and the engine runs perfectly now. Before suggesting this might be your exact issue, could you share: Current mileage on your S3, When did these symptoms first appear, Are there any other warning lights besides check engine, Does the problem get worse when the engine is hot or cold, Have you had any recent work done on the engine This information would help determine if your case matches my experience.

Thanks for checking. My S3 has 28556 KM and had its last service 3 months ago. The symptoms appeared suddenly last week. The car stalling happens mostly when the engine is cold. The check engine light is the only warning light active right now. The crankshaft sensor values look off when scanned with an OBD reader. Recent work only included regular oil and filter changes during the service. Based on your feedback about the encoder wheel, I might need to have both camshaft position sensors checked properly. Would a complete sensor testing package be worth it before replacing parts?

Thanks for those details, that additional information helps a lot. Having gone through a similar situation with my S4, I strongly recommend getting a complete sensor testing package done. The symptoms you describe, especially the cold engine stalling and irregular crankshaft sensor readings, mirror what I experienced. While my issue ended up being the encoder wheel, a proper diagnostic test revealed the full scope of the problem. The relationship between crankshaft sensor and camshaft position sensors is crucial for proper ignition timing. The testing package at my workshop cost 120 Euro, but it saved money in the long run by pinpointing the exact issue. Without proper testing, you might end up replacing parts unnecessarily. My mechanic checked both the camshaft position sensors and the crankshaft sensor during the diagnostic process. Remember that sensor failure can sometimes be intermittent, showing more problems during cold starts as you mentioned. The fact that your engine control unit is picking up irregular crankshaft sensor values suggests there might be more going on than just a single faulty sensor. Consider having both the encoder wheel and sensors checked, sometimes the encoder wheel wear isnt immediately visible but can cause these exact symptoms. This was the lesson learned from my repair experience.

Thanks for the helpful advice. After considering the feedback, I've decided to book a complete sensor testing package at my regular workshop next week. The similarities between my symptoms and your experience with encoder wheel issues and sensor failures is too close to ignore. The irregular crankshaft sensor readings from my OBD scan, combined with the cold start problems and check engine light, definitely point toward a thorough diagnostic being the smart first step. I agree that spending 120 Euro on proper testing makes more sense than blindly replacing parts. Will share the results once I get the full diagnosis. If it does turn out to be the encoder wheel affecting both the camshaft position and other sensors, at least I know what repair costs to expect. The 695 Euro total repair cost you mentioned gives me a good baseline for budgeting.