S3 Power Loss: Throttle and Air System Issues Revealed

Having some experience with car repairs, I dealt with very similar symptoms on my 2021 RS3. The check engine light came on and I noticed the same issues, rough idle and power loss during acceleration. After taking it to the workshop, they found a defective hose connection between the fuel pump and air valve. The manifold pressure readings were off because of this air supply issue. The throttle body response was also affected, leading to those acceleration problems you described. The repair involved replacing the damaged hose and checking the entire air supply system to ensure no other components were affected. Total cost was 175 Euro including parts and labor. The fix resolved both the check engine light and performance issues completely. Before suggesting specific solutions for your case, could you share: Current mileage, When the symptoms first appeared, Any recent maintenance work, Whether the check engine light is constant or intermittent, Any unusual sounds from the engine bay This information would help determine if your issue matches what I experienced or if it might be something different.

Thanks for the detailed response. My S3 has 137615 KM and the last service was done just 2 months ago. The symptoms started appearing gradually over the past week. I noticed vacuum hoses might be the culprit since I hear a slight hissing sound near the intake manifold area, especially during idle problems. The check engine light stays constant and doesnt flash. No major work was done during the last service besides regular maintenance items. The idle problems seem worse when the engine is cold, but the power loss is consistent at any temperature.

Based on your description of the hissing sound and its location, this sounds exactly like the issue I faced with my RS3. The vacuum hoses near the intake manifold are a known weak point in our engines, and the symptoms match perfectly, especially the cold idle problems. In my case, after the initial hose replacement I mentioned before, we actually discovered that the manifold pressure was affected by a hairline crack in one of the vacuum hoses that wasnt immediately visible. The air intake system wasnt getting proper pressure readings, which explains both the rough idle and power loss. Looking back at my repair experience, I would strongly suggest having all vacuum hoses inspected thoroughly, not just the obviously damaged ones. The check engine light in our models often triggers due to incorrect air-fuel ratios caused by these vacuum leaks. A quick test you can try: with the engine idling, listen carefully around the air intake area using a piece of rubber hose as a makeshift stethoscope. If the hissing gets louder through the hose, you can often pinpoint the exact location of the leak. In my case, the total repair cost ended up being 320 Euro after replacing all questionable vacuum hoses as preventive maintenance. This was more than the initial estimate I shared, but it solved the problem permanently.

Thanks everyone for the helpful responses. I think I've narrowed down the issue based on the symptoms matching your experiences. The hissing sound and vacuum leak test suggestion makes a lot of sense given my engine stalling and idle problems. I just did the rubber hose listening test you suggested and definitely heard the leak getting louder near the back of the intake manifold. This explains the manifold pressure issues and why the engine feels rough. Going to schedule an appointment to have all the vacuum hoses inspected and replaced if needed. The 320 Euro cost estimate helps set my expectations. Much better to fix all potential vacuum leak points at once rather than having to go back multiple times. Will update once I get it sorted out. Thanks again for walking me through the diagnostic process, this helped save time and gave me confidence in identifying the likely cause before taking it to the shop.