Tom,
i had the same problem with my 2000 mustang GT. Turned out to be a loose hose. Check out
http://www.users.qwest.net/~bpsilva/loosehose.jpg
to see which hose it was. It is the one circled in yellow. once i reconnected it, no more problems. It was weird because the hose seemed rather loose, and there was no hose clamp there or anything. It must have just been bumped out of place. Let me know of you have any other questions. thebean311@hotmail.com