Audi S6 Rough Running Issues: Check Engine Alert Fix

I had a similar issue with my 2011 Audi S4 last year, and as someone with moderate experience working on cars, I can share what helped solve the problem. Initially I thought it was the crankshaft sensor too, but it turned out to be a leak in the exhaust system combined with failing ignition coils. The symptoms were nearly identical, rough idle, jerking during acceleration, and check engine light. The exhaust leak was causing incorrect readings in the oxygen sensors, which made the engine run rich. The repair involved: Replacing 2 ignition coils, Fixing the exhaust leak, Clearing the error codes, Testing the fuel injectors (they were fine) Total cost was 265 Euro for parts and labor. Since then, the car has been running smoothly with no issues. Before suggesting more specific advice, could you share: Current mileage on your S6? When was the last time you replaced the spark plugs? Are you noticing any unusual exhaust smell? Have you checked the air filter recently? This information would help determine if your issue matches what I experienced or if it might be something different.

Thanks for the responses. Currently at 54335 KM and just had the last service done 2 months ago. The rough idle is definitely getting worse, especially after checking the spark plugs today. Found quite a bit of carbon buildup on two of them. Also noticed the fuel injectors might be part of the problem since there is uneven spray pattern when testing. Going to replace all spark plugs first and see if that resolves the rough idle. Will update once done.

Based on what you found with the spark plugs, the carbon buildup definitely points toward an incomplete combustion issue. On my S4, I initially only changed the spark plugs too, but it turned out the fuel injectors were indeed contributing to the problem, just like you suspect. The uneven spray pattern from your fuel injectors is a clear red flag. After dealing with my similar issues, I would strongly recommend getting the injectors cleaned or replaced while doing the spark plugs. The carbon deposits on your plugs often indicate the fuel injectors arent atomizing properly, causing poor fuel distribution. A few key things I learned from my experience: A simple spark plug change only temporarily fixed the issue, The fuel injectors needed professional cleaning, The oxygen sensor readings normalized after fixing both issues The symptoms are nearly identical to what I experienced before the complete fix. If the spark plugs alone dont resolve it, consider having the fuel injectors serviced. The crankshaft sensor could still be involved, but start with these more common issues first. Will you be doing the spark plug replacement yourself or having a shop do it?

Thanks for all the input. After looking at the costs, I decided to tackle the spark plug replacement myself this weekend. Will also get a fuel injector cleaning kit since that seems to be a common factor based on your experience. The carbon deposits you mentioned match exactly what I found, thick black coating on two of the plugs. Already ordered a set of new plugs and picked up the cleaning supplies. The timing belt area looks fine, so that can be ruled out. Will definitely check the ignition coils while I have everything apart since accessing them is simple once the top cover is off. The rough idle at startup is a real pain, so hopefully replacing these parts will sort it out. If the problem persists after this maintenance, I will have a shop check the oxygen sensor and fuel injectors more thoroughly. Understanding the diagnostic steps has been really helpful in deciding what to tackle first. Will post an update once I complete the work this weekend.