Viano Engine Stalling and Power Loss

Those symptoms definitely point towards a fuel delivery problem. A faulty fuel regulator could indeed be the culprit. The rough idling and power loss suggest the engine isn't getting the correct fuel mixture. Have you checked the fuel pressure? That's a good first step. Also, inspect the wiring and connectors to the fuel regulator and high pressure pump. A loose connection or damaged wire can cause intermittent issues. What diagnostic trouble codes (DTCs) are you getting from your OBD2 scanner? That information could help narrow down the problem. The car sensors are giving you readings, right?

I haven't checked the fuel pressure directly, as I don't have the proper tools for that. I did inspect the wiring and connectors, and they seem to be in good condition from what I can tell. The DTC I'm getting is P0093 - Fuel System Leak Detected - Large Leak. Could a faulty fuel regulator really cause such a large leak error? I am not sure if I should replace the fuel regulator, or the high pressure pump. What do you think?

P0093 confirms a substantial fuel leak or pressure issue. While a faulty regulator could contribute, that code often points to a more significant problem within the high-pressure fuel system, possibly the pump itself. Considering the symptoms and the code, I'd strongly suspect the high pressure pump is failing. Given the complexity of the fuel injection system and the potential for further damage, I would recommend taking it to a reputable workshop for a proper diagnosis. They'll be able to perform more thorough tests and pinpoint the exact cause with certainty.

I feared it might be the high pressure pump. I took your advice and went to a workshop. Turns out, you were right! The high pressure pump was indeed defective. The fuel volume regulator issue was a consequence of the pump failure. The total repair cost was 1510€, which is painful, but at least my Viano is running smoothly again. I appreciate your help in pointing me in the right direction! Hopefully, this automotive repair nightmare is over.