Boy, does this sound familier.  From someone who has experienced this
first hand, and apparently has a perfect vanagon once again, things to
check:

1) vacuum hoses--might as well replace if in doubt (cost approx. $2, so
why not)

2) air intake boot, especially where it mates to air box, for vacuum
leak.

3) O2 sensor

4) wiring from everything to the brain, cracked or damaged wire could
EASILY be the culprit.  Bad or corroded connections can also do
this--check and clean thoroughly, wiggle wires around too, what works in
one position may not in another (sign of an internal break or bad
connection)

5) grounds, if in doubt, add a few, check for corrosion here too

6) coolant temp. sensor (a whopping $12 part)--this was the source of my
problems, it was telling the brain that the engine was too hot, thus the
brain was cutting the fuel supply

The above is the most likely sources of your problem.  Feel free to
email me personally if you need more help diagnosing your problem.  I've
got LOTS of info from very generous list members that helped me through
my troubles.

Tonya
87 Vanagon GL Wolfs
74 S. Beetle