VW Lupo Diesel Stalling + Poor Response Needs Diagnosis

Had similar symptoms with a 2004 VW Polo TDI. The rough idle and power loss were identical, especially during cold start conditions. After some diagnosis, it turned out the fuel filter heater connector had corroded, causing intermittent electrical connection. The repair required replacing both the wiring harness to the fuel filter heater and the heater unit itself. This was necessary because once corrosion sets in, simply cleaning the connections provides only temporary relief. The symptoms match your case, poor throttle response, increased fuel consumption, and occasional stalling. Your mechanic seems to be on the right track. The fuel filter heater is a critical component in diesel engines, particularly for cold weather operation. When it malfunctions, it can cause exactly these symptoms by allowing wax formation in the fuel lines during colder temperatures. Suggested checks before repair: Inspect fuel filter heater electrical connections for corrosion, Test fuel filter heater resistance with multimeter, Check fuel lines for any restrictions, Verify fuel filter replacement history This repair requires specific diagnostic equipment and expertise with diesel fuel systems. While not the most complex repair, proper diagnosis is crucial to avoid replacing parts unnecessarily.

Thanks for sharing your experience with the Polo. My Lupo had those exact issues, the stalling and terrible fuel economy were really frustrating. Since fixing the corroded fuel filter heater and refreshing the fuel lines, the cold start problems disappeared completely. Just curious, what was the final cost for your repair? My fuel system work ended up needing a few extra parts beyond the initial quote. Has everything stayed running smoothly since the fix?

My repair bill came to 95€, mainly for fixing the cable connection to the fuel filter heater. The mechanic found corrosion in the plug connector and managed to sort it without needing to replace the entire component. Since then, the rough idle issues have completely disappeared and fuel efficiency is back to normal. The fuel lines and fuel filter were inspected but turned out to be in good condition, so no additional parts were needed. The car starts perfectly now, even in cold weather, and the stalling problem is completely resolved. It has been running smoothly for several months with no signs of the issue returning. Good to hear your Lupo is also fixed now. These fuel system problems can be tricky to diagnose, but once resolved they typically stay fixed as long as the connections are properly protected from corrosion.

Glad to wrap this up and share how it all worked out. Took the Lupo to a different mechanic who really knew their stuff. The fuel filter heater was definitely the culprit, just like mentioned. Total bill came to 180€ including a new fuel filter replacement since it was due anyway. The rough idle and cold start problems cleared up right away. No more stalling issues and fuel consumption is back to normal. Really impressed with how the car runs now, feels like new. Definitely learned to trust an experienced diesel mechanic over trying to save money with cheaper options. Been about three months since the repair and all systems are running perfectly. The fuel system maintenance was worth every cent. Would recommend anyone with similar symptoms to get their fuel filter heater checked first before looking at more complex issues.