RS3 Misfire Mystery: Bad Coils Causing Rough Running

Having some experience working on these engines, I dealt with a very similar issue on my 2013 RS4. The symptoms you describe match exactly what I experienced, rough running, jerking during acceleration, and intermittent check engine lights pointing to engine misfiring. After diagnostic testing, it turned out one fuel injector was defective, causing inconsistent fuel delivery and combustion misfire. Had all fuel injectors tested and one was definitely not performing correctly. The workshop replaced the faulty injector, which resolved the issues completely. Total repair cost was 515 Euro including parts and labor. The symptoms you describe could be related to several components, ignition coils, spark plugs, or fuel injectors. Before jumping to conclusions, would be helpful to know: Have you had any diagnostic codes read? Does the misfire happen more at specific RPM ranges? Is fuel consumption notably higher than usual? Any unusual sounds when the engine is idling? Have you recently used lower grade fuel than usual? This information would help narrow down whether your issue matches what I experienced with the fuel injector failure or if it might be something else in the ignition system.

Thanks for the detailed response. Just had my 63161 KM service last month and never experienced issues until now. After reading diagnostic codes, it shows consistent misfiring in cylinder 2. The check engine light started flashing during hard acceleration. Fuel consumption increased by about 15% over the past weeks. The engine misfiring happens mainly above 3000 RPM and gets worse under load. Idle feels slightly rougher than normal but no distinct knocking sounds. Always used premium fuel as recommended. Given these symptoms, seems like it could be either a failing ignition coil or spark plug issue rather than fuel injectors. Will probably start by testing the ignition components in cylinder 2 since the codes point specifically to that one.

Thanks for providing those additional details. Based on your description, especially the RPM-specific misfiring and the codes pointing to cylinder 2, this does sound more like an ignition coil issue rather than the fuel injector problem I had. The rough idle and increased fuel consumption are typical signs when the combustion process is compromised. When I dealt with my fuel injector issue, the symptoms were more consistent across all RPM ranges, unlike your RPM-specific misfiring above 3000. In your case, focusing on cylinder 2 makes sense. Testing the ignition coil and spark plug in that cylinder is a good starting point, especially since: The misfire is isolated to one cylinder, Problems worsen at higher RPMs, The issue developed suddenly rather than gradually If the ignition coil tests bad, replacing just that one could solve it. However, considering the mileage, it might be worth replacing all coils as preventive maintenance since they typically wear at similar rates. Recent experience suggests coil replacement costs around 280 Euro for parts and labor. Keep in mind that a failing ignition coil often leads to incomplete combustion, which explains both your rough idle and increased fuel consumption.

Thanks for providing such detailed advice about the ignition coil problem. Just had the repairs done today and wanted to update on the outcome. You were right, it was definitely the ignition coil in cylinder 2. The mechanic tested all components and found the coil was failing under load, exactly as described. Ended up replacing all ignition coils since the others showed signs of wear. Also changed the spark plugs while everything was apart. Total cost came to 295 Euro including parts and labor. The engine now runs perfectly smooth with no rough idle or misfiring issues. Acceleration is back to normal with no jerking or power loss. The check engine light has stayed off during several test drives. Really glad I focused on the ignition system rather than jumping straight to fuel injector replacement. The symptom pattern matching, especially the RPM-specific issues, helped pinpoint the problem. Appreciate the guidance that helped save time and money on unnecessary repairs.