A high idle speed results when the secondary throttle plates fail to close completely on some 1957 Fords equipped with the Ford four-barrel carburetor. The condition is due either to a rough edge at the flat part of the plate diameter or to a bent throttle shaft.
To correct the sticking, take off the carburetor and remove the air horn, secondary booster venturi, and the secondary throttle plates and shaft.
Polish the rough edge of the plates with crocus cloth and remove any burrs on the bore of the secondary throttle shaft. Remove only enough material to obtain a smooth fit. Polish the throttle shaft with a crocus at the three body contact points. Reassemble and install.
If the secondary throttle plates still do not close fully, install a new main body.