Clean out the idle air bypass valve, the ports it attaches to, and the throttle body & throttle valve (butterfly) with some good quality throttle body & air intake cleaner (STP makes some good stuff). Don't use regular carb cleaner. You might find a toothbrush a big help, especially if this is the first time you've done it. After that, check TPS voltage. You should have a consistent voltage of about 0.80-0.95V, without any variation or wavering, between the center wire on the harness and ground. You have a speed density EFI system, so resetting the computer and idle speed shouldn't be necessary as on later MAF systems. When's the last time you did a complete tune-up? This includes plugs, cap, rotor, wires, and possibly coil (TFI coils are so cheap, I replace mine if there's any doubt). If you want to, you may wanna have the ignition module checked by an auto parts store, just to be sure. Check your ignition timing while you're at it, too.
Okay, yeah, I'm a little obsessive about this, but I like my 'Stang to run well.
------------------
Capri306, Moderator, The Mustang Works Online
"PROUD TO BE AN AMERICAN!!!"