VW Sharan TSI: Engine Knock Causes Power Loss

Having intermediate experience with VAG engines, I dealt with similar symptoms on my 2014 VW Tiguan 1.4 TSI. The engine knock and detonation issues you describe match what I experienced, including the power loss and jerking during acceleration. In my case, the main culprit was carbon deposits in the combustion chamber, which led to pre-ignition problems. The build-up was causing irregular combustion and piston slap, triggering the knock sensor warnings. The repair involved: Complete cleaning of combustion chamber, New spark plugs, Fuel system cleaning, ECU diagnostic check and reset Total cost was 425€ and resolved the issues completely. The engine ran smooth afterward with no more knock sensor warnings. Before suggesting specific solutions, could you share: Current mileage, Fuel type typically used, Service history, especially timing of last spark plug change, Any recent engine work done, Whether the problem started suddenly or developed gradually This information would help determine if your situation matches what I experienced and whether you might need similar repairs.

Last service was at 66000km and mileage currently shows 68724km. You are spot on regarding the knock sensor concerns. After reading your detailed response, I checked my maintenance records and noticed the spark plugs were never changed since purchase. The issue developed gradually over two months, starting with minor jerking during acceleration. I have consistently used premium 98 octane fuel, yet the engine tuning seems off, particularly during cold starts. Based on your solution path, I will schedule a combustion chamber cleaning and get those spark plugs replaced first. Seeing nearly identical symptoms gives me hope this can be resolved without major engine work.

After resolving similar issues on my Tiguan, I can confirm that neglected spark plugs and carbon buildup are often the root cause of knock sensor warnings and poor engine performance. The gradual onset you describe matches my experience exactly, it started with subtle jerking that progressively worsened. The fact that you are using premium fuel is good, but with the original spark plugs at 68000km, they are well overdue for replacement. The factory recommended interval for our 1.4 TSI engines is typically 40000km. My ignition timing issues cleared up immediately after the combustion chamber cleaning and new plugs. The engine tuning returned to normal, and the knock sensor stopped detecting irregular combustion patterns. Pre-ignition problems completely disappeared. Quick tip: While they are cleaning the combustion chamber, have them inspect the cylinder heads for any scoring. In my case, there was minimal wear, but it is worth checking since we have nearly identical engine configurations and similar symptoms. The repair cost I quoted earlier included labor, but prices may vary. The most important thing is addressing it now before the pre-ignition causes more serious engine damage.

Thanks for the detailed responses. I wanted to follow up and share that I got the repair done yesterday. You were right about the spark plugs, they were completely worn out and causing the pre-ignition issues. The technician found significant carbon deposits in the combustion chamber during inspection. Complete service included: New spark plugs, Full combustion chamber cleaning, Fuel system service, Knock sensor diagnostic check Total came to 390€ and the engine runs perfectly now. No more jerking during acceleration, power is back to normal, and the check engine light is off. The ignition timing is spot on and the engine sounds much smoother, especially during cold starts. The cylinder head inspection showed minimal wear, which was a relief. Will definitely stick to the recommended 40000km interval for spark plug changes from now on to prevent these issues from recurring. Thanks again for helping diagnose the problem and sharing your experiences. The repair process went exactly as described and fixed all symptoms.