2001 Screeching noise and rpm increase

This has happened 3 times. The first and second times were about 2 weeks ago on a colder than average day. Had been driving at around 45 mph and I pushed the clutch pedal in and the RPM's went to just over 2000 and stayed there for about 20 seconds while at a traffic light. The next traffic light I came to the car did the same thing. I thought well maybe my size 12 shoes were pressing on the accelerator pedal and dismissed it as that. Then today while driving it did the same thing only this time I heard a kind of screeching sound like a electric motor would make binding up. I punched the accelerator and the noise stopped and the idle went back to normal. All three times it has done this it happens after driving a steady speed and when I depress the clutch pedal. anyone have any ideas?

The car did the same thing today. I was in the drive thru line at wendys. Moved forward and the loud humming noise started and car revved to 2500 rpms. This time punching the pedal would not stop it. I had to turn the car off so I could order food. Once started idle was normal but when I was leaving the pick up window it started again. I just drove it and after a few seconds the humming stopped and all was good again. After I ate my food I took the car on a long drive and it ran great. Wish I could figure this out. I am new to mustangs so its pretty much all french to me.

After doing a little research I believe my problem may be a bad IAC valve. From what I have read this sounds text book.

Yeah, mine looks like it has been on there awhile. I just bought the car back in september so not sure what has been replaced and what has been on there other than looks.