This problem is super familiar to me- I've had it going on over the last
year.  What I've done is basically pull the whole Idle stabilization thing
out of the loop in in terms of how the engine runs- both disconnecting the
valve itself and and the connection to the ecu.  I don't care for
air-conditioning, and I set the idle closer to 1K to deal with the power
steering. When it's cold it may need to warm up a bit, but otherwise its
fine.
    Basically, I can't figure out why the whole thing is in there. Insanely
expensive non serviceable parts that have been causing vanagon owners
problems for years (so it would seem from the archives).
    Still, I do wonder if it can be used to some advantage- will be testing
this week, actually, to find out if the bad valve or control unit is
creating what amounts to an intake leak, since air could sneak by and bypass
the throttle body this way. If that's true, I may set up the engine with the
hoses to the valve plugged. But I've done a few thousand miles without the
ISV with no noticeable ill-effect, and maybe I should leave well enough
alone.

Matt Sutton,
88 GL 114k