It could be your idle stablizer unit.....
You can get one on the net from Bus Depot for around 100.00 (I think).  I
replaced mine and cured a similar problem to the one you describe.

http://www.busdepot.com

good luck

Dane Tessler
87 Westfalia 138K
Treasure Island, FL
http://members.aol.com/Dane714/westfalia.html
-----Original Message-----
From: Goodtms4u <Goodtms4u@AOL.COM>
To: Vanagon@VANAGON.COM <Vanagon@VANAGON.COM>
Date: Wednesday, April 22, 1998 2:55 PM
Subject: Vanagon Blues

>This is my 1st posting.  I have a 85 Vanagon which runs great before it
warms
>up.  Then the idle speed occilates betwwen 900 & 1800 rpms.  It also loses
a
>lot of power and sometimes it's hard to pull away from a stoplight.  At the
>next stoplight it will perform normally.  This is my 1st wasserboxer so I
know
>nothing at all about one.  If anyone could provide some input I would sure
>appreciate it.
>