It is probably the idle stabilizer unit.  I sell these for $24 and they are
often bad.  This unit can be found on the driver's side firewall with two
round plugs going into it and it is either green or black.  Plug the two
plugs together (while the van is off).  The idle smooths out then the
stabilizer is bad, if it still lopes then you have a vacuum leak.  Hope this
helps.

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