I found something interesting last night when I was working on my Jetta. (applies to Vanagons too)  After replacing the heater hoses, the car ran so badly that it was undrivable.  After about an hour of looking under the hood and reading the Bently manual, I found that I had broken three ground wires that I think are related to the fuel injection computer.  After fixing this, the car ran better than it ever has in the 10 years I have owned it!

I assume that some fault in the ground connection had caused the engine to run a bit lean.

I'm sure the Vanagon's fuel injecton system would react differently to a bad ground than the Jetta's did, but I'm going to check all the grounds on it too.

Bill