Sounds like it might be the temperature sensor on the head.
BTDT  They sometimes become an open circuit when hot and then
as the engine cools the problem goes away for a while.  On the
type IV engines the ECU shuts down completely if that input is
open.  In an emergency you can simply ground the wire that
goes to that sensor.

Larry A.
ex 411  & 412 owner

---- Original message ----
>Date: Wed, 5 May 2004 02:20:58 EDT
>From: Pete Moore <Pete952@AOL.COM>
>Subject: engine problem
>To: vanagon@GERRY.VANAGON.COM
>
>'80 Westy - less than 5 K on rebuilt engine - has developed a
"take a rest"
>attitude. It runs like a champ for 15, 30 or 120 minutes then
just quits - dead
>- nothing. Let it sit for 15 to 30 minutes and it fires up
and goes until it
>quits again - no cough or sputter - just dead. This thing has
been in the "Air
>cooled VW Specialists" shop for - I don't want to admit how
much time and
>replacement parts ( a bunch). All the hull sensors have been
replaced at least
>once and the last time the repalaced the distributor ( it is
a CA car). I think
>it might be one of the several sensors on the engine itself
but can't put any
>consistency to it - after one quit - bout 20 min - it climbed
4000' at a
>steady 8% grade (east side of Yosemite) - then quit when it
leveled out at 9000' -
>rested and started again then ran smooth down to 2000' where
I stuck it back
>in the shop and called for my F150. They thought they fixed
it - not! I cannot
>define any consistency with elevation, load, weather,
terrain, etc. The damn
>thing just seems to have a mind of its own and wants to rest.
Not too cool on
>mountain roads with minimal shoulder or Baja with no shoulder
at all in the
>hills. Any suggestions would be greatly appreciated.
>
>Thanks for any thoughts, Pete