VW Fox Diesel Running Rough, Air Intake Troubleshooting

Had similar symptoms on a 2008 VW Polo 1.9 TDI. The check engine light combined with rough idle problems pointed to a vacuum leak in the air supply system. The manifold pressure sensor readings were inconsistent, which helped diagnose the issue. The main problem was a deteriorated hose connection between the vacuum pump and intake valve. These rubber hoses tend to crack and lose elasticity over time, especially around the 150000km mark. A failing connection creates an unstable air intake, causing the engine to run poorly. This is a serious issue that needs proper attention, if left unchecked it can lead to further engine damage and increased fuel consumption. The repair involved replacing the complete hose assembly and checking all surrounding connections. The check engine light cleared after the fix and the rough running completely resolved. Would suggest checking all visible vacuum lines first, look for cracks or loose connections. A proper diagnosis with pressure testing equipment will confirm if this matches your symptoms. This type of air intake problem is fairly common on VW diesels from that era.

Thanks for sharing your experience. Actually ran into the same issue with my 2006 VW Fox last winter. The check engine light kept triggering and engine stalling became a real headache, especially during cold starts. After reading your post, I also got the vacuum lines checked and found a significant air leak affecting the manifold pressure. The mechanic discovered multiple worn hoses that needed replacement, plus a faulty air valve that was stuck partially open. Would you mind sharing what the repair cost in your case? Just wondering if prices have changed much since. Also, has everything stayed fixed or have you noticed any other issues pop up related to the air intake system? Getting it resolved properly really improved the engine performance, but would be good to know what to watch out for going forward.

Just wanted to update on costs since you asked, I paid 175€ for the complete air valve repair on my VW Polo last month. The main issue was indeed that failing hose connection from the vacuum pump to the intake valve that I mentioned before. The repair has held up perfectly since then. The engine runs smooth with no air supply problems, and the manifold pressure readings are now stable. I make a point to regularly check all vacuum hoses for signs of wear, but have not noticed any new issues with the air intake system. One tip: now that your air valve and hoses are fixed, make sure to keep the air filter clean and changed on schedule. This helps maintain proper air flow and prevents extra stress on the new components. Good to hear you got yours sorted too. These vacuum system repairs really make a noticeable difference when done right.

After seeing these helpful replies, I wanted to share how my repair journey ended. Took my Fox to a certified VW shop last week, total bill came to 220€ for replacing the vacuum lines and air valve. More than expected but worth every cent. The mechanic showed me how the old air intake components were completely worn out. The manifold pressure was way off due to multiple air leaks. Engine stalling issues disappeared right after the repair. Really glad I asked here first, helped me understand the problem before going to the shop. The mechanic confirmed everything mentioned about the common vacuum line failures in these engines. At least now I know what warning signs to watch for if the air supply system starts acting up again. For anyone else with similar symptoms, definitely get those vacuum lines checked early. Waiting only leads to more expensive repairs down the road.