RS4 Power Loss and Knocking: Critical Warning Signs

I had a very similar issue with my 2020 RS5 last summer. Having some experience with performance cars, I initially thought it might be related to fuel octane, but it turned out to be more serious. The symptoms matched yours exactly, reduced power, jerky acceleration, and visible smoke. After the check engine light came on, I took it to a specialist workshop. Their diagnostic revealed significant deposits in the combustion chamber, which was affecting ignition timing and causing knock sensors to trigger. The fix involved: Complete combustion chamber cleaning, Spark plug replacement, Engine tuning adjustment to compensate for carbon buildup, ECU reset Total cost was 425 Euro, but it completely resolved the issue. The car runs perfectly now with no more jerking or power loss. Before suggesting specific solutions, could you share: Current mileage, Type of fuel you typically use, Any recent changes in driving patterns, Complete error codes stored, Whether the smoke is black, blue, or white This information would help determine if your issue is identical to what I experienced or if there might be other factors at play.

Thanks for your detailed advice. My current mileage is 83446 KM and the car had its last service just 2 months ago. The engine knock symptoms you described match my situation perfectly. The smoke is definitely black and occurs mainly under load. I started recording the engine sound and the pre-ignition noise is quite noticeable when the knock sensor gets triggered. I will follow up with a workshop visit and request them to check for carbon deposits, as this could explain the detonation issues I am experiencing. Will share the complete error codes once I get them properly scanned.

Thanks for the additional details. Since you mentioned recording the pre-ignition noise, I can confirm that matches exactly what I experienced with my RS5. The black smoke under load, combined with the knock sensor activation, strongly suggests carbon buildup affecting the combustion chamber efficiency. My workshop actually showed me the carbon deposits they removed during cleaning, it was surprising how much had accumulated even with regular maintenance. The deposits were creating hot spots in the combustion chamber, leading to premature detonation and that characteristic piston slap sound you recorded. One thing I forgot to mention from my experience: the black smoke significantly reduced immediately after the carbon cleaning, even before they adjusted the engine timing. This confirmed that improper fuel combustion from deposits was the root cause. Given your similar mileage to when my issues occurred, and the matching symptoms, I strongly suspect you are dealing with the same problem. Make sure the workshop specifically checks the knock sensor readings during their diagnosis, as this helped pinpoint the issue in my case. The combustion chamber cleaning alone made a huge difference in performance, eliminating both the engine knock and power loss issues. Would definitely recommend getting this checked soon before the detonation potentially causes more serious damage.

Thanks for providing such detailed information about your RS5 experience. I can confirm that my situation sounds nearly identical. After your mention of carbon deposits in the combustion chamber, I checked my service records and realized my car is due for a carbon cleaning service anyway. The black smoke and engine knock symptoms are most concerning, especially since the piston slap noise has become more noticeable during acceleration. I scheduled a workshop appointment for next week. Based on your feedback, I specifically requested they check for carbon buildup and perform a thorough combustion chamber inspection. I will make sure they examine the knock sensor readings and check for any detonation issues during diagnosis. The total repair cost of 425 Euro seems reasonable considering the comprehensive work performed. I hope my fix will be similarly straightforward. Will update once I get the diagnostic results and error codes. Really appreciate the detailed breakdown of your experience, it helped narrow down the likely cause of my engine problems.