RS6 Knock Sensor Issue Causes Rough Idle and High Fuel Use

I had a similar issue with my 2013 RS4 last year. Having some experience with basic maintenance and diagnostics, I initially thought I could diagnose it myself when the check engine light appeared with those exact symptoms. The rough idling and increased fuel consumption had me worried, especially since I noticed the engine running less smoothly at higher RPMs. After attempting basic checks, I decided not to risk further damage and took it to a workshop. Turned out the problem was a loose wiring connection to the knock sensor. The workshop found that the cable harness connector had worked itself loose over time, causing intermittent signal issues. The repair was straightforward, they secured the connection properly and checked the entire wiring harness for any other potential issues. Total cost was 95 Euro for diagnostic and repair work. While knock sensor issues might sometimes be safe to drive with briefly, I would not recommend continuing to drive with these symptoms. Poor ignition timing due to faulty knock sensor signals can potentially cause engine damage if left unchecked. Could you share some additional details about your RS6: Current mileage, When was the last service done, Any recent work performed, Are there any other warning lights showing, Does the rough idle occur more at cold start or when warm This information would help determine if your situation matches what I experienced and provide more specific advice.

Thanks for sharing your RS4 experience. In my case, mileage is at 175623 KM and the last major service was just 2 months ago. No other recent work has been done. The engine knock seems more pronounced during cold starts, and the check engine light remains steady. The decreased fuel efficiency is particularly noticeable on my daily commute, Im using about 15% more fuel than usual. Im leaning towards getting it checked soon, especially after hearing about the potential engine damage risks you mentioned. Good to know it might just be a wiring issue, though Im worried the repair costs might be higher on the RS6 platform. Would you recommend using an OBD scanner first to confirm if its actually the knock sensor before taking it to a shop?

This issue definitely sounds similar to what I experienced. While my RS4s repair was straightforward, youre right that the RS6 platform can sometimes involve more complex fixes, but an OBD scan is absolutely worth doing first. After my experience, I bought a decent OBD scanner which helped confirm the knock sensor malfunction indicator before visiting the workshop. The scanner showed error code P0325, which pointed directly to the knock sensor circuit. This helped me communicate more effectively with the technicians and potentially saved diagnostic time. The cold start symptoms you describe match exactly what I dealt with, the poor performance and engine knock were always worse until the engine warmed up. The 15% drop in fuel efficiency is also a telltale sign that the engine timing isnt optimized, likely due to the knock sensor issues. Since your car recently had a major service, its worth mentioning to the workshop as the sensor connection might have been disturbed during that work. In my case, the loose connection was actually traced back to recent maintenance. Quick tip from my experience: If you do get an OBD scanner, make sure to check for pending codes as well as active ones. Sometimes knock sensor issues can trigger multiple related codes that help paint a fuller picture of whats going on.

Thanks everyone for the detailed responses. After reading through the feedback, I decided to invest in an OBD scanner first. The scan revealed code P0325, confirming the knock sensor issue that many of you suggested. The auto repair shop just checked it out, turns out it was indeed a wiring harness problem similar to the RS4 case mentioned. They found the connection had worked loose during my recent service. Total repair cost came to 180 Euro, a bit more than the RS4 but still reasonable. The poor performance issues and rough idle are completely gone now. Fuel efficiency is back to normal too. Really glad I didn't wait longer, as the check engine warning was definitely pointing to something that could have caused more serious problems. For anyone else facing similar symptoms, the OBD scanner was definitely worth getting. It helped confirm the issue before taking it to the shop and saved time on diagnostics. Just make sure to address these knock sensor problems promptly to avoid potential engine damage.