High idle on a cold engine is normal.
You should have a motorcraft 2150 carburetor, it will have a choke plate at the top of the carb that closes when engine(choke spring) is cold, this can also have a cam that holds the throttle plate(bottom of the carb) open a little more at idle until engine(choke spring) warms up.
If the choke spring is broken or out of adjustment this cam can become loose and moves while driving so when you come to idle again it idles high, a tap on the pedal releases the cam so idle goes to normal.
A loose throttle plate can act the same way, doesn't close all the way, unless tapped.
Because tapping the gas pedal works to reduce the idle it sounds like a mechanical issue.
Google: Motorcraft 2150 2V Carburetor theory
Nice page with pictures and suggestion on how this carb works