I am no expert,  but I had a similar problem...

It was the idle stablizer thingy...located at the throttle linkage on the
engine.

Replacement part was anywhere from 170 to 200K.  I yanked one off a Vanagon
in a junkyard for 75.00 and it immediately fixed the problem.  No tools were
required.

Regards.

Dane Tessler
87 Westfalia 138K
Treasure Island, FL
http://members.aol.com/Dane714/westfalia.html
-----Original Message-----
From: Chris Pittack <chrisp@MOSAIX.COM>
To: Vanagon@VANAGON.COM <Vanagon@VANAGON.COM>
Date: Wednesday, April 08, 1998 11:28 AM
Subject: Idle Problem (87 Wasserboxer)

>Hey there,
>
>I'm having a unique idle problem.  Here's the story:
>
>Dead Cold:  Starts right up, idles at 1,100 for a few seconds and then
>drops to 800...no problem.  Never touched the accelerator.
>
>Start driving and between Dead Cold and 1/8 warm on temp gauge, will not
>maintain idle.  Drives fine but won't idle.  After it stalls it's hard
>to start but will eventually catch. You can get it to idle if you very
>slowly bring the RPM's down to idle with the accelerator pedal.
>
>Warm:  Idles perfectly!
>
>Any ideas...thanks-a-bunch.
>
>Chris P.
>Seattle, WA
>'89 Diesel Jetta "Jake"
>'87 GL Wasserboxer "Rosa"
>'82 Diesel Vanagon "Billie-Rae"