A2 Engine Knocking and Power Loss Signals Major Trouble

Previously dealt with similar symptoms on a 2005 A3 1.6L. The knock sensor warning combined with power loss pointed to severe detonation issues. After inspection, the root cause was heavy carbon deposits in the combustion chamber combined with incorrect fuel octane usage. The repair required removing cylinder heads to clean severe carbon buildup. Engine knock was happening due to hot spots created by these deposits, causing pre-ignition. Performance dropped because the engine computer was pulling timing to prevent damage. Key findings during repair: Thick carbon deposits on intake valves, Compression test showed uneven readings, Piston slap became evident once heads were removed, Spark plugs showed signs of detonation This was a serious repair requiring several days of work. The symptoms match your A2 case closely, power loss, jerking, and smoke often indicate similar combustion chamber deposits. Would strongly recommend having a compression test done first before any repairs begin. For prevention: using higher fuel octane and quality fuel system cleaners helps avoid deposit buildup that leads to engine knock.

Thanks for the detailed feedback on fixing a similar knocking issue. Your description of carbon deposits causing pre-ignition really matches what my A2 is doing. Had mine checked yesterday and the compression test also showed inconsistent readings. Since engine knock is such a serious issue, would be helpful to know what the total repair cost was in your case? Also curious if the detonation problem ever came back after the fix. Planning to use higher fuel octane going forward to prevent future issues with carbon buildup, but wondering if there are other maintenance tips you discovered.

Great to report back. After getting the combustion chamber deposits cleaned out professionally, the knocking and detonation issues never returned. The total repair cost came to 425 Euro, which included the full cleaning service and compression testing. The piston slap sounds completely disappeared once the carbon buildup was removed. For maintenance, switching to premium fuel made a huge difference. The engine computer no longer needs to adjust ignition timing to compensate for poor combustion. A few other tips that helped maintain proper combustion: Regular fuel system cleaning every 15000km, Keeping up with oil changes using manufacturer spec oil, Not letting the engine idle for extended periods, Running the engine at proper operating temperature The knock sensor now operates normally without triggering warnings. Using quality fuel really is key to preventing those harmful deposits from forming again in the combustion chamber. The investment in better fuel costs less than dealing with another major carbon cleanup.

After getting advice here, I took my A2 to a reputable shop for proper diagnosis. The mechanic confirmed severe pre-ignition issues caused by carbon deposits, just like others described. The knock sensor warnings made sense once they showed me the buildup in the cylinder heads. The full repair came to 580 Euro, which included: Complete carbon deposit removal, New spark plugs, Compression testing, Engine tuning adjustments Been running it for 2 weeks now and the engine knock is completely gone. No more jerking during acceleration or smoke issues. The engine feels much smoother and has its power back. Started using premium fuel and scheduled regular fuel system cleanings to prevent future carbon buildup. The mechanic showed me proper warm-up procedures to maintain good combustion. Definitely learned my lesson about prevention being cheaper than major repairs. Really appreciate the guidance from everyone here. Helped me understand the problem and get it fixed right instead of getting ripped off again.