Audi A2 Diesel: Rough Idle Points to Knock Sensor Fix

I had a very similar issue with my 2006 Audi A3 diesel. With some experience working on cars, I can tell you these symptoms often point to connection problems. The poor performance and check engine light in my case were caused by a loose wiring connection to the knock sensor. The car problems started exactly like yours, rough idle and increased fuel consumption. Initially thought it needed a new sensor, but the actual fix was much simpler. My workshop found the root cause quickly, a damaged wire and corroded plug connection to the knock sensor. Total repair cost was 95 Euro, mainly labor for testing connections and replacing the wiring harness connector. Before suggesting more specific advice, could you share: Any diagnostic codes from the check engine light? Does the rough idle happen more when the engine is cold or warm? Have you noticed any other warning lights? Any recent maintenance or repairs done? This information would help determine if your issue matches what I experienced. These Audi diesels often have similar patterns when it comes to sensor connection problems.

Had it checked at my last service at 124778 KM. The diagnostic showed a P0325 code, which confirms the knock sensor issue others mentioned. The rough idle is definitely worse when the engine is cold, especially in the morning. No other warning lights showing besides the malfunction indicator. In my case, the engine knock gets more noticeable during acceleration. Took a look under the hood and noticed some oil residue near the sensor connector, which might explain the connection issues. Cleaning the connector area could be worth trying before replacing the entire sensor. Would appreciate specific input about cleaning methods for the knock sensor connector, as I might try this basic fix first before booking another workshop visit.

Thanks for the extra details about the P0325 code and symptoms. Your situation sounds exactly like what I dealt with on my A3. That oil residue you mentioned near the connector was also present in my case and definitely contributed to the connection problems. For cleaning the knock sensor connector, here is what worked for me: 1. Used electrical contact cleaner spray 2. Carefully cleaned the connector pins with a small brush 3. Applied dielectric grease after cleaning to prevent future corrosion However, while cleaning helped temporarily, the ignition timing issues and poor performance returned after about a week. The warning light came back too. Turned out the oil contamination had already caused internal corrosion in the connector. The permanent fix required replacing the wiring harness connector and cleaning the sensor mounting area thoroughly. Since we have basically the same setup, I strongly suggest having the entire connection checked professionally. The knock sensor itself was actually fine in my case, it was all about the wiring and connector. Watch out for worsening performance or unusual engine noise if you decide to delay the repair. Poor knock sensor signals can lead to incorrect ignition timing adjustment over time.

Thanks for sharing those cleaning steps. I checked out the connector again and the oil contamination looks pretty severe, there is visible corrosion on several pins. Given what you described about your experience, I probably should not waste time with just cleaning since the damage seems similar to your case. I will book it in next week to have the wiring harness connector replaced and get them to properly clean the whole mounting area. The fuel efficiency drop is getting expensive anyway, and I do not want to risk further engine problems from incorrect knock sensor readings. My mechanic quoted 120 Euro for the repair including parts and labor, which seems reasonable based on what you paid. Hopefully this fixes both the poor performance and the check engine light. Will make sure they check for any oil leaks too, since that seems to be what caused the connector issues in the first place. Really helpful to hear about your actual fix confirmation rather than just throwing parts at it. Pretty sure we have identified the root cause of my car problems now.