VW Eos Knock Sensor Causing Rough Idle and Poor MPG

Had similar symptoms on a 2010 VW Passat diesel. The rough idle and increased fuel consumption matched exactly what you describe. After running diagnostics, the malfunction indicator pointed to knock sensor issues, but the actual problem was more complex. The knock sensor itself was functioning, but the wiring harness connecting it had deteriorated, causing incorrect ignition timing signals. This created the engine knock and poor fuel efficiency. The repair required replacing the entire wiring harness assembly since the cable connection was defective at multiple points. This is a serious issue that needs prompt attention because incorrect knock sensor readings can lead to engine damage if left unchecked. The faulty signals cause the engine management system to adjust timing incorrectly, which explains your current symptoms. The repair process involved: Complete diagnostic scan, Removal of intake manifold to access the harness, Installation of new wiring assembly, Recalibration of knock sensor, Reset of engine management system Many assume the knock sensor itself is bad, but often the wiring is the real culprit. Best to have a thorough inspection of the entire knock sensor circuit rather than just replacing the sensor.

Thanks for sharing those details about the wiring harness fix. Your symptoms do sound identical to what I experienced with my Eos. After dealing with poor performance and constant check engine warnings, I also thought it was just the knock sensor. My mechanic ended up finding corroded wiring and a failing connector behind the intake manifold. Would you mind sharing what the total repair cost was in your case? Also curious if youve had any engine knock issues since the fix? My auto repair should be scheduled soon and trying to get a rough cost estimate.

Since having the knock sensor issue fixed on my Passat, I have experienced zero engine knock problems. The repair turned out to be much simpler and cheaper than initially expected, just 95€ to repair the cable connection and faulty plug that was causing the malfunction. The warning light disappeared immediately after the fix, and the engine has been running smoothly ever since. This was a relief since I originally worried about needing a complete knock sensor replacement or extensive ignition timing adjustments. The check engine warning hasnt returned in the months following the repair, and fuel consumption is back to normal levels. Looking back, having an experienced mechanic diagnose the exact connection issue rather than just replacing parts saved both time and money. The auto repair was straightforward once the actual problem was identified.

After getting your feedback about the wiring harness, I took my Eos to my local mechanic last week. The check engine light and rough running were really worrying me, but the diagnosis matched what you experienced. They found corroded wiring connections and a damaged harness near the knock sensor. The total repair came to 280€, including labor for accessing the intake manifold area. More than your repair cost, but still better than replacing multiple components unnecessarily. The auto repair took about 3 hours total. The car runs perfectly now, no more engine knock during idle and fuel efficiency is back to normal. Really glad I asked here first rather than just replacing the knock sensor blindly. The proper diagnosis definitely saved me from potential future problems and unnecessary parts replacement.