Fast idle question

[players02GT]

My mustang is usually pretty good at idling around the normal 700/800rpm or so, but there have been a few instances recently (5 or 6 over the past 3 months) that the idle will sit up around 1200 and will not come down. This happened friday night when it was only about 65 degrees out. It seems to happen after I come off of the highway. And the problem corrects itself if I keep driving. If I turn it off and restart it immediately the problem still exists. If I shut it off and leave it for a while it will start with the rpm's where they should be. One time it even was to the point when I was driving and pushed in the clutch the rpms did not drop at all. And when I tapped the throttle to see if it would come down it revved up and stayed at the new higher rpm. Finally I got the rpms down by shifting in to a higher gear and force the rpms to come down. Then it ran fine for the rest of the time. That was about 2 months ago and has not done that since. Any ideas what might be causing this? The throttle body seems to move open and close like normal. Maybe the answer to the problem is really obivous, but I am not seeing it.

[Stormwalker]

Alright, I will try to help because the same thing was kind of happening to my car, but I am not sure the fix will be the same. There are spring thingys on your throttle body (the cable actually), and if they get dry and slightly oxidized, they will not return the throttle all the way, so if you lightly oil them, then your throttle might act normal again. Not sure if this is your problem though, since your car is a heck of a lot newer than mine, but you could try it, never know.

[PHRANQUY]

Could be an IAC problem too...

[RayK]

There are dual springs on the throttle. One on the TB and also on the cable itself. If the throttle returns to the TB stop, it's the IAC putting air into the intake side of the system. Either you have a vacuum leak somewhere, or the IAC is dirty and needs to be replaced. 42 bucks at Ford for the part or you can clean it, but the problem will come back sooner.

[MisterCMK]

Have you tried cleaning your IAC? I've had IAC problems with my car, my old car, and our expedition. Check that first, take apart the MAF and clean it. \