Originally Posted by Diesel911

My Car had a similar issue when I first bought it. It turned out to be way too much slack in the Throttle Linkage.
Ounce I took out as much slope as I could it ran fine.
One of the causes can be the Plastic Bushing behind the Bell Crank on the Fire wall could have gone bad.
(Engine Cold and not on) Grab hold of the Throttle Arm and hold it have someone step slowly on the Accelerator Pedal and see how much play there is in the linkage before it starts trying to move the Throttle Lever.
Release the Lever and have some on push the Accelerator Pedal all the way down and see if the Throttle Lever actually moves all the way to the Stop Screw.