If your van is carburated then you have a European model and I can't help you.
If not then your problem is either your idle switch (which is on the bottom
of the throttle body) or you idle stabilizer unit (which is behind the tail
light on the passenger side).
The switch should click when you move it to full throttle and also when you
allow the throttle to return to idle slowly (you should be able to hear it
click).  If it doesn't then remove the throttle body and flip it over and you
will see the switch on the bottom.
You can tweak the switch if it is still good (check for continuity when
closed).  Just use a pair of needle nosed pliers and tweak the little arm on
the switch a little so that when the throttle is closed or full open it
clicks.  Worked for me.  That little plastic cam on the bottom of the
throttle wears to the point it won't close the switch (or the throttle body
itself is worn to the point where shaft is wobbling around).  If it is just
the cam wear problem then the tweaking will work.  If not then you may be in
the market for a good, used throttle body (new they are around $500 US from
the dealer).
Hope this helps.

Thanks,
Ken Wilford
http://www.vanagain.com
John 3:16
Office (856)-765-1583
Shop (856)-327-0027
Fax   (856)-327-2242