Idle control module, or a vacuum leak (hook up a vacuum gauge).  Try to find an ICM to borrow for testing, they are expensive. It's mounted way behind the right tail light. Not a very good location for a computer that is not waterproofed.

Stuart

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Don Hanson
Sent: Sunday, December 21, 2014 8:43 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Isolating an idle problem?

I've been seeing an intermittent low idle-sometime no idle with my Digifant
84 van 92 rabbit/fox/Jetta ecu, etc.  This condition is occasional, when not happening, the engine behaves normally, my fuel consumption has not changed.
  My normal idle is about 900 rpm.  Recently I have had the idle decide to run at around 400 rpm...it seems to be smooth, but 400 rpm is too low and now the motor sometimes dies down there.  When I cycle the key and re start, it will again run at the low idle...no "reset"... I have a new temp II sensor and new plugs...the old plugs read normal.  My idle control thingy hums as normal and I have no obvious new vacuum leaks. Multiple different fuel sources.  Throttle switch seems to conform to the Bentley, though I have so far only  check ed the mechanical, I have not run any electronic diagnosis yet.
  Anyone want to suggest the most likely cause to this sometimes dying of my Digifant inline? Tia, Don Hanson