Sounds like your throttle position switch is either bad or not adjusted
properly.  With the van off you should hear a click when you move the
throttle to full position and then another click when the throttle is slowly
returned to idle position.  If it doesn't click then you need to adjust it
per Bentley or it may be bad or the small plastic cam that works the switch
could be worn out (happens alot).  You might be able to get away with
tweaking the arm on the switch to compensate for a worn cam (I've done it a
few times with success).  I have the throttle position switch available if
you need one.  Hope this helps you.

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