I think the problem with no replies is no one has had that problem.
Personally I answer things I know about but I dont know anything about pre OBDII (1995 or older) Fords fuel injection.
A lot of the guys on here have diesels and V-10s or newer V-8 vans with OBDII and can use a scanner for problems like that.
Did you check the blink codes? It should have at least one.
It sounds like a vacuum leak at least on the cars I know about that would be the problem.
Oh I just found this maybe it would help.
http://www.f150online.com/forums/v8-eng ... -5-8l.html
Good luck..please post what fixes it even if know one replies.. then if nothing else we might be able to help the next time..