S3 Engine Knock Crisis: Performance and Smoke Issues

I faced nearly identical issues with my 2019 RS3. Based on my experience working on various VAG engines, this sounds very familiar. The symptoms you describe match exactly what I encountered, power loss, jerking, smoke, and engine knock sensor readings. The root cause in my case was carbon deposits in the combustion chamber, which led to irregular combustion patterns. The repair involved: Complete cleaning of combustion chamber, Adjustment of engine tuning parameters, Testing fuel octane requirements, Recalibration of knock sensors Total cost was 425 Euro and resolved all issues. Performance returned to normal immediately after. Before jumping to conclusions though, could you share: Current mileage, Fuel type typically used, Any recent modifications, Exact error codes from the ECU, When symptoms first appeared This info would help determine if your situation matches what I experienced with the cylinder heads and combustion chamber deposits. Regular maintenance and using proper fuel octane ratings can prevent these issues from recurring.

Had my last service at 45000 KM and can confirm I consistently use premium 98 octane fuel. The error codes from the ECU are P0303 and P0304, suggesting cylinder 3 and 4 misfires. The issues started about 2 weeks ago, becoming more noticeable during hard acceleration. Engine knock became increasingly audible, especially when the engine is under load. I have not made any modifications to the engine tuning or performance components. The piston slap noise I mentioned earlier seems most pronounced during cold starts. Would these additional details help confirm if my issue matches your diagnosis?

Thanks for the additional details. The error codes P0303 and P0304 definitely align with what I experienced in my RS3. The fact that you are getting misfires in adjacent cylinders, combined with the piston slap noise during cold starts, strongly suggests the carbon deposit issue I encountered. The knock sensor readings in my case also showed similar patterns, increased detonation under load and during hard acceleration. Even with premium fuel octane ratings, carbon buildup can create hot spots in the cylinder heads that cause irregular combustion. A few key observations that match our cases: Multiple cylinder misfires, Knock sensor activation under load, Issues worsening with acceleration, Clean service history, Proper fuel usage The repair procedure I mentioned earlier should resolve these symptoms. The technicians will likely need to inspect the cylinder heads for carbon deposits and verify the knock sensor readings are not due to mechanical wear. Would you be able to notice if the piston slap noise has gotten louder over time? This detail helped diagnose my case.

It's concerning to hear the piston slap noise has indeed gotten progressively louder over the past few days. The symptoms you described match my situation perfectly, especially the knock sensor behavior and misfires in cylinders 3 and 4. My mechanic appointment is scheduled for next week. Given the matching symptoms and error codes, I will ask them to specifically check for carbon deposits and pre-ignition issues in the combustion chamber. The ignition timing might need adjustment as well, based on your experience. The repair cost of 425 Euro seems reasonable considering the work involved. I am relieved to hear that proper cleaning and recalibration resolved the issues without major mechanical repairs to the cylinder heads. I will update once I get the diagnosis confirmed. Thanks for sharing your detailed experience. It helped narrow down the potential causes and gave me a clear direction for the repairs.