Same problems with my vivaro too. Found it to be caused by a tiny hole in the fuel pipe. The pipe had been rubbing on the engine mount just after the fuel filter in the engine bay. It had a sleeve around the pipe so I cut that off and cleaned it with some liter fuel and raped some tape around it for now. Just bin for test drive and it now starts first turn, pulls all the way through the revs and its not cutting out. Hope this helps some of you.