[Pyrotechnic]

A clean set of injectors metering the proper amount of fuel will definitely help. Just running some injector cleaning through your tank of often not enough to clean them, but the ultrasonic cleaning can break the dirt loose. A 20+ year old set of injector is most likely due for a cleaning.

As for the bottom portion, it wouldn't hurt to check yours out first. The throttle shafts may not be worn out at all. Take it off and see if the play is excessive.

My plan of action would be the check the throttle shafts, and if that is OK simply rebuild it myself with a set of professionally cleaned or new injectors, whichever is cheaper.