I have a 91’ with the same layout. I replaced the TPS twice. One was defective the other was a pain in the butt to figure out but I did get a good lead on how they work. For one thing these sensors are made of plastic and after dissecting the old one I saw how sensitive these can be (and for the 68$ it’s a piece of junk) However either use it or convert to a carb?? but the symptoms are identical and the sensor may be good just over tightened when installed. (easy to do) but while over tightening the mounting screws, the mech. has distorted the unit. (could be a warped component or the throttle body is warped… I the later being a long shot.)
(btw checking the grounds is a good idea… I have three)
The trick is that the original had a soft gasket (primarily a dust gasket but pliable for mounting) The two inside wires facing the motor of the three wire connector handles about 20 milliamps of current. The easy test is back off the mounting screws put a volt meter on Ohms and watch the readout while moving the throttle in it’s full range. And only tighten the mounting screws so that full range tests out. You can put a light dab of soft gasket material that will later cure but I didn’t bother.
Since the condition occurs intermediate after warming up (I experienced the same) Again, these sensors are so flimsy with tiny ribbon cables and a metal contact, it’s very easy for these to get warped while the engine is warm, too. To repeat, back off those screws and check for full throttle movement. e.g. if the readout quits at any point with no tension from the mounting screws… the TPS is defective.
Sorry you had to buy the air/mixture motor… the TPS works in conjunction with the motor. The old one may have been fine as I have 189k miles on mine and I cleaned the throttle body and ports.