'90 Ford econoline sputters and stalls when first moving.?

Idle air valve needs to be cleaned. Usually this is part of the throttle body and it is easy to remove (if anything is easy to access on a van). Clean it with carb cleaner, wipe it off, and put it back. Also, Fords sometime need the idle stop screw turned in (clockwise) a quarter turn or so to correct idle issues. If you do this and it idles too fast then you turned it too far.