1992 Ford F150 starts and idles ok, release gas pedal and i

Engine Mechanical problem
1992 Ford F150 V8 Two Wheel Drive Automatic

you get in, start the truck and everything is ok, it runs a little rough though. once you use the gas pedal its still ok, but one you release it the engine will not return to idle, its revs go down until it stalls. Ive checked and its not the torque converter