Have you been able to figure out the exact reason the throttle won't return to the home position when the pedal is released?

When you move it to the home position by hand under the hood, does it fully close and remain in that position? Or does it pop back up to a higher idle when you take your hand off of the linkage?

If it stays put, just install a stronger return spring. If it pops back up when you take your hand off of the linkage, something is forcing it up. You need to find whatever it is.

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)