My apologies to the list members for sending this out in HTML format.  Here
it is in plain text so it can be read.

There are a number of possibilities as other list members have suggested.  I
had the same problem and it took me a long time to find the cause in my
case.  After replacing most of the ignition system to no avail, I
disassembled the distributor. There is a roll pin that you need to work
with.  What I found was a very sticky grease between the shaft and the plate
holding the timing pickup.  It would sometimes grab and move the timing off
causing the engine to quit.  After a few minutes with the engine stopped
(the time varied) it would release with the spring pulling it back into
place and the van would run just fine until the next time.

Cleaning the shaft and lubricating with a silicone grease and installing it
back into the engine solved the problem.  This was at least 6 years ago.  No
problem since.

Have a look and let us know what you find.

Larry Stichweh