Audi S1 Stalling: Bad Fuel Causing Rich Mixture Issues

Had similar issues with my 2019 Audi S3. The check engine light came on and the car showed unstable idle symptoms matching yours. The fuel mixture was running too rich and causing stalling. The root cause turned out to be a faulty oxygen sensor connection. The wiring harness had corroded at the connection point, causing incorrect readings and making the engine computer adjust the fuel mixture incorrectly. This is a serious issue that needs proper diagnosis. While bad fuel quality can cause similar symptoms, the consistent error code suggests a component problem rather than contaminated fuel. In my case, the fuel filter was also clogged, likely from previous poor fuel quality, which compounded the rich fuel mixture problem. The repair required: Cleaning corroded connector pins, Replacing the wiring harness section, Installing a new oxygen sensor, Replacing the fuel filter, Performing ECU adaptation After the fix, idle stability returned to normal and fuel economy improved significantly. Would recommend having it properly diagnosed rather than continuing to drive with these symptoms, as rich fuel mixture can damage other components over time.

Thanks for detailing your S3 experience. Your symptoms do sound very similar to what I am dealing with. Mine started showing the exact same behavior, unstable idle and engine stalling. The fuel system issues you mentioned make a lot of sense, especially since the engine knock became noticeable right after that questionable fuel station visit. After reading about the corrosion in your oxygen sensor wiring and clogged fuel filter, I am starting to think fuel contamination might have triggered cascade issues in my combustion chamber too. Do you remember roughly how much the complete repair ended up costing? Also, has everything stayed problem-free since the fix or did you notice any other issues popping up later?

Thanks for asking about the repair costs. Since having the mechanic fix the wrong fuel mixture issues last month, my S3 has been running perfectly with zero problems. The total bill came to 95 Euro for replacing the corroded cable connection on the oxygen sensor. Much cheaper than I initially feared! The unstable idle and engine knock symptoms completely disappeared after addressing the incorrect fuel composition. The mechanic confirmed the fuel system was showing signs of contamination, but catching it early prevented any serious engine damage. The repair has definitely been worth it, fuel economy is back to normal and the engine runs smoothly at all speeds. No check engine lights or other issues have appeared since the fix. Would definitely recommend getting yours checked soon to prevent any cascade problems from developing in the fuel system.

Thanks for the info. After dealing with the same headaches, I finally took my S1 to a different mechanic last week. The diagnosis showed similar issues to what you experienced, contaminated fuel system and sensor problems leading to the wrong fuel mixture. The repair involved cleaning the fuel system, replacing the fuel filter, and fixing a loose oxygen sensor connection. Total cost was 280 Euro but the engine knock and stalling are completely gone. Fuel economy has improved noticeably too. Much better experience than my previous mechanic who just kept resetting the check engine light without fixing the underlying fuel quality problems. This new shop took the time to properly diagnose everything and explain the cascade of issues that developed. Really glad I switched mechanics and got it sorted before any major engine damage occurred.