S4 MAF Sensor Failure Symptoms and Fixes

I had a very similar issue with my 2006 A4 and can share my experience as someone with moderate car repair knowledge. The symptoms matched exactly what you describe, poor fuel economy, engine stalling at idle, and performance decline. The check engine light was also constantly on. After dealing with this for about a week, I took it to a workshop for diagnosis. The mechanic confirmed it was indeed a mass air flow sensor failure. The repair cost was 365 Euro total, including parts and labor. After replacement, the engine ran smoothly again and fuel consumption returned to normal. Before going to the workshop, you can try cleaning the existing MAF sensor with specialized cleaner, sometimes this resolves the issue. However, if cleaning doesnt help and the symptoms persist, replacement is likely needed. For more specific advice, could you share: Current mileage on your S4, When symptoms first appeared, If you notice the issues more during cold or warm engine conditions, Any other warning lights besides check engine, Whether youve had similar sensor failures before This information would help determine if your situation matches what I experienced and allow me to provide more targeted suggestions.

Thanks for the detailed reply. My S4 is at 89901 KM and had its last service 3 months ago. The initial cleaning of the mass air flow sensor showed improvement for about a week, but then the check engine light came back on. The air-fuel ratio seems off again, as the smoke and poor performance have returned. The engine stalling happens more frequently when the engine is warm, especially at traffic stops. I have checked the air filter, and it appears clean. No other warning lights are visible on the dashboard besides the check engine light. Based on your experience, it sounds like I should proceed with replacing the MAF sensor. Did you notice any immediate difference in engine performance after the replacement?

Thanks for the additional details. Yes, I noticed an immediate improvement in my A4 after the MAF sensor replacement, the engine ran noticeably smoother within the first few kilometers. Your symptoms mirror my experience exactly, especially the temporary improvement after cleaning and issues returning. When my air-fuel ratio was off due to the faulty MAF sensor, I also noticed the stalling was worse at operating temperature. The fact that your air filter is clean but problems persist strongly suggests the mass air flow sensor is the culprit. In my case, the new sensor resolved: The unusual engine stalling, Excessive fuel consumption, Smoke during acceleration, The persistent check engine light The workshop confirmed my air intake system was otherwise fine, and the MAF sensor replacement fixed all issues. Given your mileage and symptoms, particularly the failed cleaning attempt, replacement is likely your best option. The repair cost should be similar to what I paid (around 365 Euro). Just ensure the workshop performs proper diagnostics first to confirm the MAF sensor is definitely failing before proceeding with replacement.

I appreciate all the information and your feedback about the MAF sensor replacement experience. Given the similar symptoms and especially how the cleaning only provided temporary relief, I feel more confident about proceeding with the replacement. The consistent check engine light, combined with the engine stalling and poor performance, matches your experience too closely to ignore. Since my air filter is clean and the issues persist, the MAF sensor does seem to be the likely culprit. Good to hear you saw immediate improvements after the replacement. The quoted cost of 365 Euro seems reasonable for parts and labor, considering the complexity of the repair. I will schedule an appointment with my workshop next week to have them run diagnostics and likely replace the sensor. Thanks for helping confirm my suspicions about the mass air flow sensor failure. It has been helpful to hear from someone who dealt with such similar symptoms and got them resolved through replacement.