VW Fox Diesel: Power Loss & Engine Stalling Symptoms

I had almost the exact same symptoms with my 2008 VW Polo diesel about 2 years ago (speaking from moderate experience with diesel engines). The symptoms you describe strongly point to a faulty injection valve. In my case, the poor air-fuel ratio was causing the engine management system to constantly adjust the fuel mixture, leading to those exact issues, power loss, rough idle, and jerking during acceleration. My workshop diagnosed it through their diagnostic computer and found one injector was delivering inconsistent fuel amounts. They confirmed this by testing the return flow rates from each injector. The repair involved replacing the faulty injector, which cost 515€ including parts and labor. After the fix, the engine ran smoothly again with proper throttle response and no more check engine lights. Could you share: Current mileage on your Fox? Are you getting any black smoke from the exhaust? Does the problem get worse when the engine is warm or cold? Have you noticed increased fuel consumption? This information would help determine if your symptoms match what I experienced and could point to whether its likely the same injector issue. Also, while checking injectors, its worth having the mass airflow sensor tested as it can cause similar symptoms when failing.

With 66066km on the clock, I can confirm these exact symptoms. After checking with my workshop during last month's service, they found the mass airflow sensor was contaminated and the oxygen sensor had failed. Both were affecting the air-fuel ratio significantly. The check engine light would come on intermittently, especially during cold starts. The rich mixture caused poor performance and rough running. Replacing both sensors resolved all issues completely and cost 380€ total. Before spending money on injectors, get these sensors tested first. They are cheaper to replace and often cause similar symptoms in these engines. The rough running and power loss disappeared immediately after the repair. No more check engine light since then.

Thanks for sharing your experience. Your Fox had exactly the same symptoms as mine, and I agree that checking sensors first was the smart move. Just to add to my previous comments about the injector issue, before replacing my injector, I also had the oxygen sensor tested but it was fine in my case. Your intake manifold setup is identical to mine, and these engines are known to be sensitive to any air-fuel ratio imbalances. The fact that your mass airflow sensor was contaminated actually makes a lot of sense, these sensors often get dirty over time and send incorrect readings to the engine management system. Since fixing my injector, I have made it a habit to use high-quality fuel and change the fuel filter according to schedule. This has kept the engine running smoothly without any rich mixture issues or sensor problems for the past 2 years. For anyone else reading with similar symptoms: start with checking the oxygen sensor and mass airflow sensor before assuming injector problems. The diagnostic steps and repair costs you shared are pretty typical for this model and could save others from unnecessary expensive repairs.

I see everything is working perfectly now after addressing those sensor issues. The rough running and power loss problems were exactly what others described, and getting the mass airflow sensor cleaned and oxygen sensor replaced was definitely more cost-effective than jumping straight to fuel injection repairs. Our car runs great since fixing those components. The check engine light has stayed off, acceleration is smooth again, and the engine maintains steady power. Looking back, the symptoms were classic signs of sensor problems affecting the air-fuel mixture. For anyone else with a similar issue, have your workshop test the sensors first before assuming more serious problems. The total repair cost of 380€ was reasonable compared to major fuel system work. Just make sure to use quality fuel and keep up with regular maintenance to prevent these issues from recurring. Running properly now with 66066km on the clock and no more rough idle or power issues. The throttle response is back to normal and the engine performs exactly as it should. Definitely worth getting those sensors checked early when similar symptoms appear.