Somewhere in the connection between the accelerator pedal and the throttle body, there's slop. When depressing the throttle, response is very poor until the pedal makes it to the floor - then the car functions properly.
I am pretty sure it's linkage. Fuel is good, new filter and screen, 40+ pounds fuel pressure, new ignition wires and plugs, no codes, etc. But the car doesn't GO!!
Are you sure there is slop in the linkage? Have you been able to actually look at things as they are moving? Could be the TPS out of adjustment for one thing. The only areas of possible slop would be the throttle pivot and cable to the pedal as long as the cable anchor points are OK. IMO
The cable is non adjustable so if there is any slop in the cable something is grossly wrong. Have you watched the TB end while someone depresses the peddle? I can't imagine that the cable has stretched that much. As long as each outer sheath end is anchored properly and the throttle peddle mechanism is not loose or worn. Then it has to be the inner cable. Are you sure it is routed correctly to the TB? Not sure if it's possible to screw that up but if it's possibly routed where the cruise control cable goes????? Have any pics?
This '88GT has 40k miles on it, but spent most of its life stored unprotected, in the sun. I got it running, and it passed CA smog. There are many small problems still to be resolved, including this throttle issue.
I compared the visible throttle linkage (throttle body) to drawings, and at that end of the cable it's correct. I still have not figured out how to reliably post photos here.
Tonight I plan to recruit my wife to push the gas pedal as I observe the linkage. That might identify the source of the problem (as opposed to the TPS, etc.).