VW Polo TDI Rough Idle and Poor MPG After Sensor Fix

Had similar issues with my 2014 VW Golf 2.0 TDI. The check engine light and rough idle turned out to be a damaged wiring harness connector at the crankshaft position sensor. The connector had partially melted, causing intermittent signal issues. The symptoms match exactly, poor fuel efficiency, rough running, and warning light. Initial diagnosis suggested knock sensor, but deeper inspection revealed the actual issue. The damaged connector was interrupting ignition timing signals, leading to the engine running inefficiently. This is a serious issue that needs proper diagnosis, incorrect ignition timing can potentially cause engine damage if left unchecked. The repair requires specific knowledge of VW diesel electronics and proper diagnostic equipment. Recommend having these checked: Wiring harness condition, especially near hot components, Sensor connections at the engine, Full diagnostic scan for timing-related fault codes, Physical inspection of knock sensor wiring For VW diesels, always ensure the shop has experience with TDI-specific diagnostic equipment and certified training for diesel systems.

Thanks for sharing your experience with the Golf. I faced nearly identical car problems on my Polo last summer, the check engine warnings and terrible idle made me think the engine was about to give up. After checking the engine codes, they also blamed the knock sensor at first, but it turned out to be a clogged fuel filter causing poor performance. Did you remember roughly what the repair ended up costing you? Also curious if youve had any similar issues pop up since getting it fixed? My auto repair took about 300€ total but would be interested to compare notes on the final bill.

Thanks for asking about the repair costs. Since seeing the mechanic last month, the knock sensor issue has been completely resolved. It was exactly as initially suspected, a faulty connection in the wiring that was disrupting the sensor signals and causing those performance problems. The final bill came to 95€ for fixing the defective cable connection at the knock sensor. This was much more reasonable than expected, especially compared to your fuel filter repair. The warning light hasnt returned and the engine is running smoothly again with proper ignition timing. The poor performance and rough idle symptoms completely disappeared after the repair. Looking back, the intermittent nature of the problem clearly pointed to an electrical connection issue rather than a mechanical fault. No similar car problems have occurred since the fix, the engine response and fuel economy are back to normal. Just make sure any mechanic doing this type of repair has the right diagnostic equipment to properly test the sensor connections. Getting an accurate diagnosis early can save a lot of trouble and expense down the road.

I took my Polo to a different mechanic this week after reading about the wiring issues mentioned here. The malfunction indicator had me worried, but turns out the problem was simpler than expected. They found a loose connector causing erratic signals to the engine control unit, affecting the ignition timing. The repair took about 2 hours and cost 180€ including diagnostic time. The check engine light is now off and the rough idle is completely gone. Fuel efficiency has improved dramatically, already seeing about 15% better consumption on my daily drives. The mechanic showed me the faulty connection and explained how it was causing the issues. Much better experience than my previous repair attempt. The car runs like new again, and I learned to always get a second opinion when the initial diagnosis doesnt feel right.