VW Lupo Running Rich, Common Causes And Solutions

I had a similar issue with my 2004 VW Polo, which shares many components with the Lupo. Based on some experience working on VWs, these symptoms often point to fuel delivery problems. In my case, the fuel injectors were indeed the culprit. The mechanic found that one injector was stuck partially open, causing a constant rich mixture. The oxygen sensor readings confirmed this, showing the air-fuel ratio was way off. After replacing the faulty injector and testing the others, the problem was completely resolved. The total repair came to 515€, including parts and labor. The symptoms you describe, rough idle, excessive fuel consumption, and jerky acceleration, match exactly what I experienced. The rich mixture was causing incomplete combustion, which explained the power loss. Before proceeding with repairs, it would be helpful to know: How many kilometers are on your engine? Have you noticed any black smoke from the exhaust? When was the last time your spark plugs were replaced? Has the check engine light been scanned for error codes? These details would help determine if your issue is indeed similar to what I encountered with the injectors.

Thanks for sharing your experience with the injector issues. My Lupo just had its service 2 months ago, but these symptoms started appearing last week. I have not noticed black smoke, but fuel economy has dropped significantly. I will get the error codes scanned tomorrow. When they checked the intake manifold during my last service, everything looked clean, so I was hoping it might be something simpler. The oxygen sensor seems like a good place to start diagnosing, given your experience with faulty injectors causing similar symptoms. Did you notice any specific error codes when your injector was stuck?

Thanks for the follow-up info. Yes, when my injector was malfunctioning, I got the P0172 code which specifically indicates a rich fuel mixture. Given that your Lupo was recently serviced and the intake manifold is clean, you might be dealing with a different root cause than I had. The oxygen sensor might indeed be the first thing to check, since a faulty O2 sensor can send incorrect signals to the ECU about the air-fuel mixture. In my case, before replacing the injectors, we actually tested the oxygen sensor to rule it out. The sensor test showed the injectors were the problem, but the symptoms can be very similar. Since no black smoke is present, this could point more toward an oxygen sensor issue rather than stuck fuel injectors. A bad O2 sensor typically costs less to replace than injectors, around 150-200€ compared to the 515€ I paid for my injector work. When you get the error codes scanned, look specifically for: P0171-P0175 codes related to fuel trim, P0130-P0135 codes which indicate oxygen sensor issues, P0300 series codes that might show misfires These codes will help determine if your situation matches what I experienced or if its heading in a different direction.

Thanks for the detailed codes and pricing info. The scan showed P0172 like you mentioned, along with P0134 for the oxygen sensor circuit. Your case definitely helped me narrow down where to look. Since my symptoms match what you experienced with the fuel injectors, but I also have that oxygen sensor code, I will have both components checked. My air filter is also due for replacement according to the service schedule, so I will get that done at the same time to eliminate any air intake issues that could affect the air-fuel ratio. It is good to know the full injector repair was 515€ in your case, helps me budget for potential repairs. I will update once I know which component was causing the rich mixture. The check engine light and poor performance are definitely motivating me to get this sorted quickly.