Have you checked if the throttle body housing is dirty and the throttle not closing fully?

Could be TPS, find which is signal wire and test it with meter, should be around 0v with closed throttle, smoothly going up to 4-5v on full throttle.

Maybe some adjustment on the TPS, not sure,as I haven't worked on one of those for many years!

Is there any adjustment on the throttle for base idle?