10 to 1 it's the IAC (Idle Air Control motor). My car did the EXACT same thing. What that is, is a little needle (pintle) that moves by an electric motor through a pinhole that allows air into the system. This pinhole becomes becomes clogged with gunk and blocks the path for the air coming in.
For some reason, the dealer always skips this in place of the MAF and everything else. The MAF makes a better buck. The IAC is just a matter of removing two screws (thoe bottom being a beitch), and shooting some Valvoline Throttle Body cleaner in there and cleaning off the pintle.
On my 95SE 2.5 Duratec, the IAC is located just front of the firewall, drivers side middle. It's right around where the other air-intake ito the manifold is (the other being your main intake).
