S4 Rough Running + Fuel Waste Points to Rich Mixture

Recently dealt with similar symptoms on my 2015 Audi A4 2.0T. The fuel economy dropped drastically and the engine had rough idle and hesitation issues. It turned out the fuel injectors were failing, causing uneven fuel distribution. The diagnosis revealed carbon buildup was preventing proper atomization, leading to rich fuel mixture. The oxygen sensor readings were also inconsistent, which explained the check engine light. Initial tests showed the catalytic converter was getting excess fuel due to the faulty injectors. This was a serious issue requiring complete fuel injector replacement. Leaving it unfixed risks damaging other components like the catalytic converter and oxygen sensors. The symptoms match your description, especially the power loss and jerky acceleration. Before taking it to a shop, check if the air filter is clean and ensure youre using the correct fuel grade. However, given the age and mileage, its likely the fuel injectors need professional attention. The repair involves specialized diagnostic equipment to properly test injection patterns and fuel pressure. Consider getting the carbon deposits cleaned while the injectors are being serviced. This helps prevent similar issues from recurring and improves overall fuel economy.

Thanks for sharing your experience. I had very similar symptoms with my S4 last year, rough running, awful gas mileage, and jerking under load. My issue ended up being failed spark plugs and a faulty oxygen sensor that was causing the engine to run way too rich. The air filter was also pretty clogged when they checked it, which definitely wasnt helping the situation. Everything improved dramatically after replacing those components. Do you remember roughly what the total repair cost was for your injector work? Also curious if youve had any other issues pop up since getting it fixed? Always good to know what else to watch out for with these engines.

Good news, I got the fuel injector issue completely resolved. The repair came to 515 Euro for replacing the faulty injection valve that was causing the rich fuel mixture. Since the fix, the engine runs perfectly with no more issues with excess fuel consumption or rough running. The fuel economy has returned to normal and the hesitation during acceleration is completely gone. The work included proper calibration of the new injector and verification of the fuel pressure. No issues with the oxygen sensor readings anymore either. Unlike your case where spark plugs were the culprit, my catalytic converter was starting to get damaged from the rich condition, but catching it early prevented any permanent damage. Having a proper diagnosis made all the difference, the faulty injector was causing significantly more fuel to be delivered than necessary. Its been about 6 months since the repair, and the engine has been running flawlessly. No check engine lights or other problems have emerged. The shop also cleaned the intake while they were in there, which helped restore optimal performance.

I finally took my S4 to a reputable performance shop last week after gathering all this helpful advice. Turns out I had multiple issues causing the rich mixture, two clogged fuel injectors and carbon buildup in the intake manifold were the main culprits. The total repair came to 890 Euro including parts and labor. They cleaned the intake manifold, replaced the problematic injectors, and did a full fuel system cleaning. The check engine light is now gone and the car runs like new again. The shop showed me the carbon deposits they cleaned out, it was pretty shocking how much buildup there was. The fuel economy has improved dramatically and the jerky acceleration is completely resolved. They mentioned regular fuel system cleaning could help prevent similar issues in the future. While not cheap, at least I know the root cause is fixed rather than just treating symptoms. The car feels much more responsive now and Im no longer worried about causing damage to other components from running too rich.