Hi My 1990 vanagon camper starts = up..runs awhile then dies on me...a little later I am able to restart it, but it happens = again....the last time I got it started it was hestiating like it was = going to die, then I was told it was letting out some black smoke from the exaust..all this started happeneng after I took it in for a oil,lube = & filter change...I noticed they cracked the air filter case and I = repaired that, but it is stil dying on me.....any suggestions??