You need to check somethings before we can diagnose your problem.  First check
to see that all of your sparkplug wires are plugged in.  If the van is idling
rough then unplug some of the sparkplug wires on the cap (becareful to only
unplug one at a time).  If the wire and plug are good then the rpm will drop.
Try this until you unplug one and the motor stays running the same.  That will
tell you which wire is not doing it's job.
Check the plugs for black sooty deposits which could cause fouling.
Check inside of distributor cap (orange thing that spark plug wires hook to)
to see if there are black carbon tracks built up in there.  If there is clean
cap with acetone or something similar and replace it.  If towers look burnt or
really chewed up then it needs to be replaced.
Also check your fuel filter.  It is a grey boxy looking filter near the fuel
tank (under the van on the sliding door side).  Unhook it and make sure fuel
is coming from the tank OK (you should have something to catch the gas in) and
tap the filter on your hand the arrow imprinted on it pointing up.  If you see
junk fall out onto your hand then you need a new filter.  Even if you don't
see junk fall out on your hand and you have never replaced this filter, now
would be a good time.
Let us know what you find.
Ken Wilford
John 3:16