My 2000 Ford Ranger revs. And when I say revs, I mean like I have the pedal to the floor, even though my foot is off completely. Pulling up on the gas pedal does nothing. The only way I can get back down to idle is to let the clutch out just a little to add a load to the 4 cylinder engine. My mechanic has tried to fix it before, and did for a while, but the problem returned.
The problem might be with a faulty Idle Air Control valve.
Locate the IAC valve on the throttle body. Start the engine and when the idle speed goes out of control, take the handle of a screwdriver and rap on the IAC valve. if doing this changes the idle speed, replace the IAC valve.