Idle issue on an 89 sidekick 8v

[Freaky Beanie]

the TB is easy to test, off car, IAC.
wife at work.? Grin
super easy, in pan of hot water.
even frying pan of hot water, with thermometer clamped to the pan, and at 150f it is 100%. closed.
are you sure you cars thermostat is good, or some goofy guy put in a silly 160F stat? (or none at all, OMG) I know it's new but currently, I am unsure on the temp rating and will take a look.
you could buy a 195 (or 193)F stat and run that and see if the IAC closes. (band aid fix)
or use the frying pan to learn exactly what temperature yours closes 100% super easy.
the cars gauges in the cluster are just toys, never use them to diagnose engines, use real measurement tools. gauges.
I use an IR gun, for $15 that works great. the truck is not ready for road yet. I just let it idle in my garage (with an exhaust fan of course) I have a FLIR IR Camera so I will test soon. (Busy weekend doing plumbing for my parents so I may only have time next week )

to RAD tank after 20+ miles 100% fully hot engine.
then idled for 15mins.