Could be a worn or glitchy throttle position sensor (number one suspect I think), or idle air controller (little solenoid in throttle body) sticking. Could also be a wiring issue that would be helped by cleaning connectors and plugs. Try cleaning all the connectors first, since it's essentially free. Finally, don't discount the linkages. There are two places where my old 87's linkages went wrong with this result. First, make sure that the pivot on the accelerator pedal itself isn't sticking. Second, make sure that the bell crank on the side of the engine, which carries the linkages to the throttle body, isn't worn and sticking. ON mine, the pivot was so badly worn that it would bind, even when lubricated. I couldn't get the stupid rusted torx bolts off (and my daughter was about to sell it anyway) so I just added a spring to the linkage to pull it back harder.