Sounds like the Vanagon Syndrome as described in the westfalia.org message
boards - look at the posts in their fuel injection section.  There's a
patch cable that plugs into the airbox available from VW and Bus Depot that
cures it sometimes, and I think there's a far cheaper and maybe just as
effective fix that involves installing a capacitor across a couple of the
airbox connector terminals.  It is described somewhere in the vanagon.com
list.  Search around, and good luck.
-Will