S1 Runs Lean: MAF & O2 Sensors Eyed in Power Loss Issue

As someone with moderate experience working on cars, I had a very similar issue with my 2016 Audi S3. The symptoms matched exactly what you describe, rough running, power loss, and the check engine light coming on. After checking the air-fuel ratio readings, my workshop discovered faulty fuel injectors were causing inconsistent fuel delivery. The intake manifold pressure readings were also erratic, which pointed to the injection system rather than sensor issues. The repair involved: Testing all fuel injectors, Replacing 2 defective injectors, Cleaning the remaining injectors, Full system diagnostics, Resetting the engine management system Total cost was 515 Euro for parts, labor and diagnostics. After the repair, the engine ran smoothly again with proper power delivery and no warning lights. To help diagnose your specific case, could you share: Current mileage, When you last had fuel system maintenance, Whether the check engine light is steady or flashing, If you notice the issues more during cold starts or when warm, Any fuel consumption changes The catalytic converter can also be affected by running lean, so catching this early is important.

Had my regular service done at 42463KM and the throttle body was inspected and cleaned during that visit. My check engine light is steady, not flashing. The jerking and power loss happen mostly when the engine is warm, especially during moderate acceleration. I also noticed higher fuel consumption lately, about 15% more than usual. My previous experiences with rough running were typically related to oxygen sensor issues, but this feels different. The engine doesnt seem to be responding correctly to throttle input.

Thanks for those details. Looking back at my Audi S3 experience, your symptoms are very close to what I encountered, but the behavior during warm running points more toward a possible EGR valve issue rather than just the fuel injectors I initially suspected. When my car showed increased fuel consumption with warm-engine power loss, the workshop found carbon buildup was preventing the EGR valve from operating correctly. This caused inconsistent air-fuel ratios, especially under load. The fix involved: EGR valve cleaning and testing, Spark plugs replacement as a preventive measure, Fuel system pressure test, ECU adaptation reset The repair cost was 380 Euro and resolved both the power loss and fuel consumption issues. The check engine light never returned. Your steady check engine light suggests this could be a similar scenario. The warm-engine symptoms particularly match, as EGR-related issues often become more noticeable after the engine reaches operating temperature. Consider requesting these specific diagnostic checks: EGR valve operation, Fuel pressure under load, Air-fuel ratio during acceleration, Carbon deposit inspection

Thanks everyone for the detailed replies. After comparing the symptoms to both suggested scenarios, I think the EGR valve theory makes the most sense for my situation. The warm-engine issues and steady check engine light match up perfectly with what was described. I booked an appointment with my regular workshop and specifically requested they check the EGR valve operation and carbon buildup, along with testing the fuel pressure and air-fuel ratios during acceleration. The steady check engine light hasnt changed, and the throttle response is still inconsistent, especially when warm. Will update once I get the diagnostic results and know exactly what components need attention. Really hoping its just carbon buildup on the EGR valve rather than a more extensive fuel system problem. The increased fuel consumption is definitely concerning, but at least the catalytic converter isnt showing any additional warning signs yet.