A3 TDI Rough Running: Chronic Misfire Mystery

After seeing your A3 TDI symptoms, this strongly reminds me of what happened with my 2009 A4 TDI. The engine misfiring and rough idle were nearly identical, particularly during acceleration when the throttle response was very inconsistent. In my case, the root cause was indeed a defective fuel injector. The symptoms started gradually, first with minor hesitation, then progressed to significant power loss and constant engine misfiring. The combustion misfire was especially noticeable during cold starts. This turned out to be a serious issue requiring complete injector replacement. The faulty injector was causing improper fuel atomization, leading to incomplete combustion. These symptoms will typically not resolve themselves and can potentially damage other engine components if left unaddressed. The repair involved: Diagnostic testing to identify the problematic injector, Removal and replacement of the faulty injector, Full system calibration, Test driving to confirm proper combustion Given your symptoms and mileage, I would strongly suggest having the injectors tested. A proper diagnosis should include checking injector spray patterns and return flow rates. This isnt a quick fix job but absolutely needs proper attention from a shop experienced with TDI engines.

Thanks for sharing your experience with the faulty injector. Had almost the exact same thing happen with my A3. After replacing the fuel injector and getting a fuel system cleaning, the check engine light finally stayed off and the throttle response went back to normal. Curious what the repair ended up costing you? Mine needed a couple extra parts while they were in there and hoping you didnt run into any other issues after getting it fixed.

Got my A4 TDI back from the mechanic last week and can happily report the cylinder misfire issues are completely resolved. The check engine light hasnt come back on since the repair, and the throttle response is perfect again. The total cost came to 515 Euro for diagnosing and replacing the defective fuel injector. This included a full system calibration to ensure proper fuel delivery. The repair shop confirmed the combustion misfires were entirely due to the faulty injector causing irregular fuel spray patterns. Unlike your case, I didnt need any additional parts or fuel system cleaning. The original diagnosis proved accurate and fixing just the injector solved all the problems. The engine now runs smoothly without any hesitation or power loss during acceleration. Its been great to have the car running properly again without that constant worry about engine misfires. These TDI engines really do need proper attention when fuel delivery components start showing signs of wear.

Thanks for the helpful advice. After taking it back to a different shop that specializes in diesel engines, they properly diagnosed the cylinder misfire. The spark plug was completely worn and the injector needed replacement. The repair took about 4 hours and cost 680 Euro total including parts and labor. The engine misfiring is completely gone now and throttle response is back to normal. No more jerking during acceleration or rough idle. The check engine light has stayed off for over a week. The mechanic showed me the old injector and you could clearly see it was causing combustion misfire issues from irregular spray patterns. They also found some carbon buildup while doing the work, so they cleaned that out which probably helped too. Really glad I got a second opinion and had it fixed properly this time. The car runs like new again and I feel much better knowing the root cause was properly addressed.