TT Running Rich: O2 Sensor vs Intake Manifold Issues

Had similar symptoms on my 2016 Audi S3 with the 2.0 TFSI engine. The check engine light came on, and the car was running noticeably rich. Rough idle, poor acceleration, and higher fuel consumption were the main symptoms. After diagnosis, it turned out one of the fuel injectors was stuck partially open, causing excessive fuel delivery. The rich mixture was causing carbon buildup and affecting engine performance. The faulty injector was constantly leaking fuel into the cylinder, throwing off the air-fuel ratio. This is definitely a serious issue that needs prompt attention. A malfunctioning injector can lead to: Cylinder wall damage, Catalytic converter failure, Further carbon buildup, Increased emissions The repair involved replacing the defective fuel injector and cleaning the intake system. The technician also checked the air filter and performed a fuel system cleaning to ensure optimal performance. While oxygen sensors can cause similar symptoms, the specific pattern of poor acceleration and constant rich condition pointed directly to the injector issue. Getting it fixed immediately prevented more expensive repairs down the line.

Thanks for sharing your experience with the fuel injector issue. Mine is still at the shop but your description matches my symptoms exactly, especially the rough idle and poor acceleration. The mechanic mentioned they need to check both the fuel injectors and intake manifold for carbon buildup. Did you remember approximately how much the repair cost you? Also curious if you had any similar issues pop up since the fix? Im hoping once this is sorted the fuel economy will get back to normal.

After getting the repair done, I can confirm it completely solved the rich mixture issue. The mechanic found and replaced one faulty fuel injector that was causing the problems. Total cost came to 515 Euro, which included the new injector, labor, and a thorough cleaning of the intake system. The engine now runs perfectly smooth, no more sluggish acceleration or rough idle. Fuel economy returned to normal levels immediately after the fix. The check engine light hasnt come back on either. Its been over 8 months now with no recurring issues. The spark plugs were also inspected during the repair and showed some carbon fouling from the rich condition, but cleaning them up as part of the service helped restore proper performance. Getting it fixed promptly was definitely worth it to prevent damage to other components like the catalytic converter. When fuel injectors malfunction like this, they can really throw off the entire fuel delivery system.

I just got my car back from the shop yesterday and wanted to update everyone. The mechanic confirmed it was indeed a stuck fuel injector causing the rich mixture, just like others mentioned. They replaced the faulty injector, cleaned out the carbon buildup, and did a full inspection of the air filter and spark plugs. Total repair came to 480 Euro, which seems fair considering the work done. The difference in performance is night and day, no more jerky acceleration or rough idle. Fuel economy is already much better after just one day of driving. The mechanic showed me the old injector and explained how it was causing excess fuel to leak into the cylinder. Really glad I didn't wait longer to get it checked out, as they mentioned the check engine light was warning about potential damage to other components. Will monitor things over the next few weeks but so far everything feels back to normal. Thanks to everyone who shared their experiences and helped point me in the right direction.