VW Lupo Diesel Intake Issues: Loss of Power & Hissing

Had a very similar issue with my 2004 VW Polo diesel and can share some relevant experience as a regular DIY car maintainer. The symptoms you describe match exactly what I encountered, especially that distinct hissing and the jerky acceleration. The intake system problems started gradually but got worse over time. Initially thought it was just normal wear, but the poor engine performance made it clear something was wrong. Took it to a workshop where they diagnosed a defective switch intake manifold control. The manifold flap was stuck, causing inconsistent airflow control and the power issues you mentioned. The complete repair including parts and labor came to 465€. The fix made a huge difference, proper acceleration returned, the hissing disappeared, and fuel consumption went back to normal. The whole repair took about 3 hours. Before offering more specific advice, could you share: Current mileage, Whether you notice the issues more during cold or warm engine, Any recent maintenance history, If you have access to diagnostic tools to check fault codes Since these intake manifold problems are somewhat common on VW diesels from that era, getting it checked soon would be wise, even without the engine light. Leaving it too long can impact engine performance and potentially cause additional issues.

Thanks for the detailed reply. My current mileage is 149900km, and had the last service 3 months ago. The engine misfire gets worse when the engine is cold, especially during morning starts. The poor engine performance is most noticeable under load, like when climbing hills or during overtaking. The intake manifold flap seems to make more noise in cold conditions. I tried cleaning the airflow control system myself but saw no improvement. The workshop quoted 490€ for diagnosis and potential repairs, which seems high compared to your experience. Before booking it in, I want to make sure this matches the typical repair cost for this issue. Would appreciate if others could share their repair costs for similar intake system problems on VW diesels.

Thanks for those details, especially about the cold start issues. That really helps confirm what we're dealing with here. The fact you mentioned poor engine performance during hill climbs and cold starts strongly points to the intake manifold flap control problem I had. The noise pattern matches too. On my Polo, the hissing got much worse in cold weather, just like yours. Regarding the 490€ quote, that is slightly higher than what I paid (465€), but still within a reasonable range. The air intake system repair costs can vary based on parts availability and labor rates. In my case, they had to replace both the flap control unit and a sensor. The workshop might be quoting higher because they are including a full diagnostic check. My initial quote was also around 500€, but came down once they confirmed it was just the intake manifold issue. Given your mileage and symptoms, this repair should resolve the engine performance issues. I noticed immediate improvements after the fix: No more cold start problems, Smoother acceleration, Normal fuel consumption returned, Hissing completely gone Since cleaning did not help, the flap control mechanism likely needs replacement. Would suggest going ahead with the repair before it affects other engine components.

Appreciate your experience with the VW diesels and the repair costs info. You actually described the symptoms perfectly, the cold weather performance issues and that characteristic hissing are exactly what I'm experiencing. The reduced power during cold starts and inconsistent engine performance definitely match up with the intake manifold flap control problems you had. I was worried the 490€ quote was excessive, but hearing about your similar repair cost makes me feel better about proceeding. I will book it in next week for the intake system repair. The air intake problems are getting worse, especially during cold morning starts, and I do not want to risk additional engine misfire issues or damage to other components. Since my symptoms match your experience so closely, I feel more confident now that this is the right diagnosis and a fair repair cost. Thanks for helping me understand what to expect with the flap control unit replacement.