Audi S8 Engine Power Issues Point to Air System Fault

Having some experience working on cars, I faced a very similar issue with my 2020 S7. The symptoms you describe match exactly what I encountered, inconsistent power delivery and that annoying check engine light. The root cause in my case was a defective hose connection from the pump to the vacuum valve. This created a vacuum leak that messed with the air intake system and throttle body response, leading to those idle problems you mentioned. My workshop ran a full diagnostic on the air supply system and pressure tested all connections. The fix itself was straightforward once identified, replacing the faulty connection. Total cost was 175 Euro and the car was ready same day. But before jumping to conclusions, it would help to know: Have you noticed any unusual sounds from the engine bay? Does the power loss happen more during cold starts? What engine variant does your S8 have? Have you scanned for specific error codes? Getting this info would help determine if you are dealing with the same issue I had or if it might be something else in the air intake system.

Last service was performed at 189000km and I can confirm the power loss happens more during cold starts, especially in the morning. The engine makes a slight whistling sound when accelerating. The error code scanner showed P0171, suggesting a lean fuel mixture. This aligns with your vacuum leak theory. Your repair experience gives me hope its a straightforward fix rather than a major throttle body issue causing the engine stalling. Thanks for the detailed insight about the diagnostic process. Will book a pressure test to check the entire air intake system.

Thanks for providing those additional details. The P0171 code and whistling sound during acceleration on your S8 match exactly what my S7 displayed before the repair. In my case, the lean mixture combined with the whistling was a clear indicator of air leaking into the intake system where it shouldnt. When the workshop pressure tested my car, they found the vacuum hoses had developed hairline cracks near the connection points, allowing unmetered air to enter. This uncontrolled air supply was throwing off the manifold pressure readings and causing the ECU to adjust the fuel mixture incorrectly. Important to note, while my repair was straightforward, have them check the throttle body while testing the system. In rare cases, the vacuum leak can cause carbon buildup around the throttle plate over time. The good news is this can usually be cleaned during the same service. The cold start symptoms are particularly telling. When vacuum hoses are compromised, the issues tend to be more noticeable before the engine reaches operating temperature, exactly as you described. Based on the identical symptoms, I strongly suspect youre dealing with the same air intake system issue I had. Get those pressure tests done and you should have a definitive answer.

Thanks for all that information about similar symptoms on your S7. The cold start issues and whistling sound definitely point to a vacuum leak, and knowing the specific P0171 code helped confirm my suspicions about the air supply system being the culprit. The manifold pressure issues you experienced match what I'm seeing. I appreciate the heads up about checking the throttle body during diagnostics. Given how my engine stalling happens mostly on cold starts, just like in your case, I'm increasingly confident it's related to those vacuum hoses you mentioned. The check engine light pattern and power delivery problems are too similar to be coincidence. I've scheduled the pressure testing for next week. If the repair cost ends up close to the 175 Euro you mentioned and can be done in a day, that would be ideal. Will make sure they inspect the entire air intake system, particularly those connection points you highlighted where hairline cracks developed. Your experience has given me a much clearer picture of what to expect during diagnostics. Will update once I get the test results back.