VW Up Engine Stalling and Power Issues Fixed

I had a very similar issue with my 2021 VW Polo last year. I have some experience working on cars but fuel injection systems require specialist knowledge and equipment. The symptoms you describe match what I experienced, rough idle, power loss, and check engine light. The fuel injection system was the culprit in my case. The workshop ran diagnostics and found one injector was defective, causing an overly rich mixture. They had to replace the faulty injector and recalibrate the fuel injection system. Total repair cost was 515€. The throttle body and intake manifold were also inspected but turned out fine. Sometimes a failing catalytic converter can cause similar symptoms, but the diagnostic tools pointed clearly to the injector in my case. Before suggesting more specific advice, could you share: Current mileage on your Up? Any recent maintenance work done? Are you getting any specific error codes? Does the problem get worse when the engine is warm or cold? This info would help determine if your issue matches what I experienced with my injector failure or if it might be something else.

Thanks for the detailed reply. My Up has 134651km on the clock. Just had it serviced last month where they changed oil, filters, and spark plugs. The check engine light showed code P0171 which points to a lean mixture condition. The problem definitely gets worse when the engine warms up, which makes me think the catalytic converter might not be the primary issue. The intake manifold also looks clean, I checked it myself last weekend. The symptoms match your fuel injection problem description. Did your workshop mention how they determined it was specifically the injector and not the fuel pressure regulator? Also curious about the diagnostic steps they took before replacement.

I see you have similar symptoms to what my Polo had, but the error code P0171 points to a lean mixture while my issue was a rich mixture. Still, the fuel injection system is likely the root cause, just failing differently. In my case, the workshop first did a fuel pressure test which showed normal readings. Then they used specialized diagnostic equipment to monitor the air-fuel ratio and injector pulse width while the engine was running. They found one injector was delivering inconsistent spray patterns, affecting the overall air-fuel ratio. The mass airflow sensor was also tested since it directly impacts mixture preparation, but it checked out fine. After replacing the faulty injector, they had to perform a fuel injection calibration to ensure all injectors were working in harmony. Your lean condition could also be caused by: Vacuum leaks in the intake system, Clogged fuel filter restricting flow, Failing fuel pressure regulator, Dirty mass airflow sensor Since your symptoms worsen with heat like mine did, I would focus on the fuel delivery components first. The total diagnostic process at my workshop took about 2 hours before they pinpointed the exact issue. The actual injector replacement was relatively quick once they identified the problem. Have you noticed any unusual fuel consumption changes? This could help narrow down whether you are dealing with a lean or rich mixture situation.

Given those additional details, I see my situation might be a bit different since I'm getting a lean code rather than rich mixture readings. The fuel consumption has actually increased by about 15% over the last month which matches a lean condition. The intake manifold check I did showed no obvious vacuum leaks, but I guess small cracks could be hard to spot visually. Since my mass airflow sensor is original with 134000km, that could definitely be contributing to the lean mixture. I will take it to the shop and ask them to follow a similar diagnostic approach, starting with fuel pressure testing and injector monitoring. Makes sense to methodically check each component rather than just throwing parts at it. Will definitely have them look at the mass airflow sensor too since that directly impacts the air-fuel ratio calculations. Thanks for sharing your diagnostic process. Even though the final fix might be different in my case, knowing what tests to expect helps me have a more informed conversation with the workshop.