1992 Pontiac Grand Prix high idel

The idle is controlled by metering the amount of air allowed into the engine. When the idle is too high, it means unmetered air is being allowing in somewhere. You have an air leak somewhere but judging by the mileage you have. I would suspect that the throttle body is so worn, that it's not capable of sealing all the air out. It's probably sucking air in through the throttle shafts and the inability of the throttle plate to fit the bore properly any more.