VW Lupo Engine Knocking and Power Loss, Fix Guide

I had a very similar issue with my 2006 VW Polo. As someone with moderate experience working on VWs, the symptoms you describe match exactly what I encountered, knocking, power loss, and detonation during acceleration. In my case, carbon deposits in the combustion chamber were causing pre-ignition problems. The workshop confirmed this after running diagnostics. They performed a thorough combustion chamber cleaning, adjusted the ignition timing, and recommended switching to higher octane fuel to prevent future issues. The total repair cost was 425€, which included: Complete chamber cleaning, New spark plugs, Diagnostic scan, Timing adjustment Since the fix, no more piston slap or knocking sounds, and the engine runs smoothly again. The higher fuel octane rating definitely helped prevent the issue from recurring. To better assist you, could you share: Current mileage, Service history, When was the last time spark plugs were changed, Any recent changes in fuel type or brand, Other warning lights or codes showing This would help determine if your issue is identical to what I experienced or if there might be other factors involved.

Thanks for the detailed response. My Lupo just had its annual service last month and has 56459km on the clock. I have not changed fuel type or brand recently. Your experience with carbon deposits sounds similar to my symptoms. The way you describe the pre-ignition issues matches what I am experiencing. The engine tuning might also need attention since the cylinder heads have never been cleaned in my ownership period. The workshop costs seem reasonable for the work performed. Will get the combustion chamber inspected and timing checked as you suggest. Have booked it in next week for diagnostics. Hope the repair costs stay within that range.

Thanks for the update on your Lupo. Your mileage is actually quite similar to when my Polo started showing these symptoms. The timing of issues right after a service is interesting, sometimes routine maintenance can stir up settled carbon deposits, leading to knock sensor issues and detonation problems. Good call on getting the cylinder heads inspected. Since you mentioned they have never been cleaned, this could definitely be contributing to the pre-ignition problems. When they did my combustion chamber cleaning, they found significant carbon buildup affecting the ignition timing despite regular servicing. Just to prepare you: the actual cost might vary slightly from my 425€ repair depending on how much cleaning is needed. My chamber cleaning took longer than expected due to stubborn deposits, but the improvement in performance was worth every cent. Consider asking them to check the knock sensor while they are at it. In my case, it was sending incorrect signals due to carbon interference, causing the ECU to adjust timing incorrectly. Would be interested to hear what they find during diagnostics next week.

The knock sensor and pre-ignition symptoms you described certainly match my situation. Thanks for confirming the typical repair costs and sharing your experience with carbon deposits. With my 56459km and recent service history, it makes sense that carbon buildup could be causing these detonation issues. I will definitely have them inspect the knock sensor during diagnostics since incorrect timing signals could explain the performance problems. I have switched to higher octane fuel for now as suggested. Will update the forum once I get the engine tuning and combustion chamber cleaning done next week. Hoping the repair costs stay around 425€, but prepared for variations depending on the carbon deposit situation they find. Makes me feel better knowing this is a known issue that can be properly diagnosed and fixed rather than something more serious. Looking forward to getting the proper engine performance back.