RS3 Knock Sensor Issues Causing Engine Problems

Dealt with an identical issue on my 2021 RS4 last summer. Having some experience with Audi maintenance, I noticed similar symptoms, poor performance, increased fuel consumption, and that dreaded check engine warning light. After monitoring the symptoms for a week, I took it to a workshop where they diagnosed a loose connection in the knock sensor wiring harness. The cable connection had deteriorated, causing intermittent sensor readings. The repair involved replacing the connector and securing the wiring properly. Total cost was 95 Euro for the repair including labor. Since the fix, fuel efficiency returned to normal and the rough idle completely disappeared. These knock sensor issues can sometimes be tricky to diagnose because they mimic other engine problems. Could you share: Current mileage on your RS3, Any recent maintenance or work done, Whether the issues started suddenly or developed gradually, If you notice the problems more during cold starts or when engine is warm This information would help determine if your situation matches what I experienced and could point toward the best solution.

Thanks for your helpful reply. For reference, my RS3 has 100799 KM on the odometer and just had its regular service done last month. The malfunction indicator appeared quite suddenly after a cold morning start. The rough idle seems worse when the engine is cold but improves slightly once warmed up. The fuel efficiency drop has been consistent regardless of temperature though. The knock sensor symptoms you described match mine exactly. Good to know it might just be a wiring issue rather than a sensor replacement. Will have the workshop check the connections first, as 95 Euro sounds much better than a full sensor replacement.

Thanks for the additional details about your RS3. The symptoms you describe, especially the cold-start issues and consistent poor fuel economy, match my experience even more closely than I initially thought. When my RS4 showed these problems, I actually tried cleaning the knock sensor connections first before going to the workshop. However, I would not recommend this DIY approach as improper ignition timing from a malfunctioning knock sensor can lead to serious engine knock and damage. After the wiring fix, my auto repair shop recommended monitoring the engine performance for about a week. The check engine light cleared immediately, but they wanted to ensure the fix addressed all symptoms. Like yours, my idle was particularly rough during cold starts before the repair. One thing to note, since your car just had service, make sure to mention this to the workshop. Sometimes knock sensor issues can occur if wiring was accidentally disturbed during routine maintenance. This might even help reduce your repair costs if it relates to recent work. Have you noticed any unusual sounds from the engine, particularly during acceleration? This could help confirm if its definitely knock sensor related rather than a different sensor causing poor performance.

I really appreciate the detailed follow-up. Yes, there is a slight metallic ticking noise during acceleration that wasnt there before. This definitely strengthens the knock sensor theory. Looking at the symptoms, rough cold starts, higher fuel use, and the check engine light, everything points to the wiring connection issue you experienced. Will bring up the recent service when booking the workshop appointment. Makes sense that the wiring could have been disturbed during maintenance. The ignition timing concerns you mentioned about DIY fixes convinced me to let professionals handle it. Not worth risking engine damage to save a few Euro. Planning to take it in next week. The malfunction indicator and performance issues are concerning enough that I dont want to wait. Will avoid any hard acceleration until then to prevent potential engine knock damage. Thanks for helping narrow down the likely cause. Good to have a realistic idea of repair costs and time frame before heading to the workshop.