VW Lupo Diesel Check Engine Light & Rough Running Fix

Had a similar issue with my VW Polo diesel from 2004. As someone with moderate experience working on VWs, I can share what helped resolve this. The check engine light and rough running were caused by vacuum hoses that had deteriorated. The connection from the pump to valve was completely worn out, affecting the manifold pressure and overall engine performance. The throttle body wasnt getting proper signals due to the compromised air intake system. My trusted workshop diagnosed it with a pressure test of the vacuum system. They found the faulty connection and replaced the hose assembly. Total cost was 175€ including parts and labor. The repair completely resolved both the check engine light and the rough running. Before suggesting specific fixes, could you share: What year is your Lupo? Does the rough running happen more at idle or while driving? Have you noticed any whistling sounds from the engine bay? When was the last time your air filter was changed? These details would help identify if your issue matches what I experienced or if its something else in the air intake system.

Thanks for sharing that experience. My Lupo is a 2005 model, last serviced at 47850km. The engine stalling and rough running mainly occurs while driving, particularly when accelerating. I have not noticed any whistling sounds, but there is a slight hesitation when pressing the throttle. The symptoms you described with the vacuum hoses sound very similar to what I am experiencing. The air supply issues and manifold pressure problems match up with how my car behaves. Did your repair shop mention any specific testing methods they used to confirm it was the vacuum system before replacing parts?

Thanks for those additional details. Since sharing my Polo repair experience, I actually encountered similar throttle hesitation issues again last month, but this time it was a different cause. The air supply problems in your case, especially during acceleration, match a common issue in these VW diesels. While my first repair involved vacuum hoses, the second time around the manifold pressure sensor itself was failing. The engine stalling during acceleration is a telltale sign. When I brought it back to the workshop, they used a diagnostic scanner that specifically monitored manifold pressure readings during acceleration. This testing method showed irregular pressure fluctuations that werent present during my previous vacuum hose issue. The repair involved replacing the manifold pressure sensor and cleaning the surrounding air intake components. Total cost was 230€, and it completely resolved the hesitation and engine stalling. Given your Lupo is from 2005, these components are in the age range where they commonly start failing. The symptoms you describe are almost identical to what I experienced the second time around. A proper diagnostic scan while the engine is running would quickly confirm if its the sensor or vacuum lines.

Thanks for the detailed information about your Polo repairs. The age of my 2005 Lupo and similar acceleration issues definitely point toward the vacuum system or pressure sensor being the culprit. The idle problems and engine stalling match exactly what you described. I will ask the shop to specifically check both the vacuum lines and manifold pressure sensor when I take it in. Knowing that the throttle hesitation could be linked to either component helps narrow down the diagnostic path. The fact that your car had different root causes for similar symptoms, but both related to the air valve system, is particularly helpful. Based on your repair costs, I should budget around 200-250€ to cover either scenario. Will schedule an appointment and make sure they do the pressure testing you mentioned. Good to know these issues are fixable and common for VWs of this age. Thanks again for sharing your experience in such detail.