Viano engine issues faulty intake air temperature sensor

Sounds familiar. I had similar engine issues with my Vito. Check that temperature reading from the air sensor. Mine was giving crazy values. Have you tried cleaning the sensor first? Sometimes that's enough. What kind of diagnostic tool are you using?

I haven't tried cleaning the sensor yet. I'm using a pretty basic OBD2 scanner. When you say 'crazy values', what do you mean exactly? Like, way off from the ambient temperature? And did your Vito have the same symptoms, reduced power and rough running?

Yeah, the temperature reading was all over the place, jumping from -40 to +80 degrees Celsius. And yes, exact same symptoms: reduced power, rough idling. Cleaning might help temporarily, but I ended up replacing the air sensor. If your diagnostic tool points to it, and you have those symptoms, it's likely the culprit. If you're not comfortable doing it yourself, take it to a workshop and save yourself the headache.

I took your advice and went to the workshop. They confirmed it was indeed the intake air temperature sensor, just like the diagnostic tool said. 155€ later, the sensor is replaced, the engine light is off, and she's running smoothly again. Your advice gave me the confidence to get it sorted quickly.