Viano diesel engine jerking and rough idle

Sounds frustrating. I had similar symptoms on my Vito jerking, rough idle, and that awful exhaust smell. Definitely check the air intake manifold. A common issue is a leak developing around the manifold sensor. Have you checked the manifold pressure readings with a scan tool? What values are you seeing at idle and under load? That might give you a clearer picture before you start tearing things apart.

Thanks for the quick reply! I did a quick check of the manifold pressure, but I wasn't really sure what the acceptable ranges are. Do you remember what readings you were getting when you had the issue, and what kind of values I should be looking for at idle and under load to confirm a gasket leak? Also, did you notice any visible scorching around the manifold itself when you inspected it?

Honestly, I can't recall the exact manifold pressure readings off the top of my head, but they were significantly off from the expected values way too low at idle, I think. I'd suggest searching online for the expected manifold pressure values for your specific engine code. Regarding scorching, I didn't see anything obvious at first glance, but once I removed the manifold, it was clear there was a gasket leak. You might be better off taking it to a decent workshop, they have better diagnostic tools to pinpoint the issue.

Thanks for the advice! I appreciate you sharing your experience. I took it to a workshop as you suggested. Turns out the intake manifold was indeed defective, with a significant gasket leak. The total repair cost, including parts and labor, came to 1180€. At least it's running smoothly again now!