A3 Misfire Mystery: Coils and Plugs Under Suspicion

I had a very similar issue with my 2011 Audi A4 2.0T last year. Having some experience with basic maintenance tasks, I first suspected spark plugs or ignition coils causing the rough idle and misfires. However, after taking it to my regular workshop, they discovered a significant leak in the exhaust system near the manifold. This was causing irregular air-fuel mixture readings and throwing off the engine timing. The repair, including parts and labor, cost me 265 Euro. The symptoms you describe with jerking during acceleration and misfires match what I experienced. The leak was allowing excess air into the system, which caused the engine management to get confused, similar to having a faulty crankshaft sensor reading. Before jumping to conclusions though, could you share: Current mileage on your A3? When was the last time spark plugs were replaced? Are you noticing any unusual exhaust sounds or smells? Does the rough running get worse when the engine is cold or warm? This information would help narrow down whether your issue might be similar to what I encountered or if it points to something else.

Latest service was done at 180000 km, about 2 months ago. Thanks for your detailed response. After reading it, I checked and noticed a slight ticking sound from the exhaust area that I hadnt paid attention to before. The rough idle is definitely worse when the engine is cold. The spark plugs were changed during the last major service 3000 km ago, but the ignition coils are original as far as I know. I am starting to think it might indeed be related to an exhaust leak like in your case, though I want to make sure the ignition coils are not the culprit since theyre original and known to fail on these engines.

Thanks for providing those details about your A3. Since you mentioned the spark plugs were changed recently, we can probably rule those out. However, those original ignition coils at 180000 km are definitely worth investigating, especially since theyre a common failure point on our 2.0T engines. That ticking sound from the exhaust area is remarkably similar to what I experienced with my exhaust leak. The fact that your rough idle is worse when cold also matches my experience, as the metal contracts more in cold conditions, potentially making any exhaust leaks more pronounced. In my case, I initially swapped the ignition coils before discovering the actual exhaust issue. If youre considering checking the coils first, you could try swapping them between cylinders to see if the misfire moves with them. If it does, then youve found your culprit. New coils typically run about 45 Euro each. However, given the similarity of that ticking sound to my previous issue, Id recommend having the exhaust manifold area checked for leaks first. The symptoms are nearly identical to what I dealt with, cold rough idle, jerking during acceleration, and that distinctive ticking sound. A smoke test would quickly reveal any exhaust leaks and save you from unnecessarily replacing parts. The timing of when these issues started also matches the typical failure period for these components on our engines.

The cold running issues and ticking sound definitely give me more to work with. After reading about your experience, I checked my service records and called my regular mechanic. He confirmed ignition coils commonly fail on these engines around my mileage. But given the ticking noise I discovered, he agreed we should check for exhaust leaks first before replacing the ignition coils. Going to book it in next week for a proper inspection focusing on the exhaust manifold area and they will do a smoke test. If that comes back clear, well move on to testing the ignition coils by swapping them between cylinders. The fuel injectors will also get checked since they can cause similar symptoms. Really appreciate your help in narrowing this down. That ticking sound might have gone unnoticed if you hadnt mentioned your exhaust leak experience. Will update once I know more about whether its the exhaust system or electrical components causing the issue.