Thanks for the advice guys. I'm going out to clean that ground and possibly just peremptively clean the FITV as suggested. Just looking to see if I can reuse the O-ring inside.

Yes I have a voltmeter and a powered digital multimeter.

I have reset the ECU backup before, but maybe if I clean that ground and the FITV, 'then' reset it, it might relearn the idle right this time...

 

I've heard of problems with that coolant-temperature sensor. If someone can find a table of resistance vs. temperature, you can measure that with your multimeter. Certainly look for flaky wiring connections. Don't confuse that with the sender for the temperature gauge in the cluster. ECT sensor has 2 wires, gauge sender has only 1 wire. Fan switch has 2 wires but it is located on the thermostat housing.

O-rings will probably be hardened and likely to leak if you re-use them. But it's a game of chance. Any gasket/seal that is really easy & painless to replace, go ahead and try it. FITV top cover will simply leak anti-freeze if that doesn't seal

But if the FITV or IACV O-rings don't seal for the air passageways, that can cause a vacuum leak, which will send you on a different wild-goose chase in the middle of this overall troubleshooting.

 

Yea I might see what size it is and scavenge one off something else. I called around, where I'm at (Spokane, WA) every parts store only sells the 'entire' throttle body / intake manifold assembly as one piece. All the guys at the stores keep saying "you can't take those things apart on your own, you need to replace the whole thing"! I'm like, "sorry, dude, don't have $400 to throw away right now..." I think the dealership sells the individual gaskets/rings but doubt they have them in stock for something as old as 93...