Viano Diesel Engine Running Lean

I had a similar issue with my Vito, though I don't remember the exact year. Reduced power and rough running were the main symptoms. Did you check the readings from your mass air flow sensor? A faulty MAF sensor can cause a lean condition by giving the ECU bad data, reducing the fuel injected. Also, what's the condition of your fuel filter? A partially blocked filter can restrict fuel flow, causing it to run lean. The oxygen sensor readings would be crucial here too, to see if the air-fuel ratio is off. A clogged EGR valve could also contribute, but it's less likely to be the main cause. How does the engine sound when idling?

Thanks for the quick reply. I checked the mass air flow sensor data, and the readings seem okay. But I'll check it again under different loads. The fuel filter was replaced about 20000 kilometers ago, but I'll inspect it again. The oxygen sensor readings do change, and I'll analyze them more closely. Was your issue caused by a bad injector, and if so, how did you figure that out?

My lean running was caused by a faulty injector. After checking the MAF sensor, fuel filter, and oxygen sensor readings, the mechanic did an injector test. This showed that one of the injectors wasn't delivering the right amount of fuel. Given your symptoms and mileage, I'd suggest getting the injectors professionally tested. It's a common issue with these engines. I took mine to a workshop, and they fixed it in a day.

I appreciate the help. I had the injectors tested, and it turned out one was bad and causing the lean running. I replaced it, and the engine runs smoothly now, with full power and no more jerking. The total cost was 515€ for the injector and labor. Thanks for your insights, they really helped me fix this.