89 firebird 2.8 700r4

Have an OTC scan tool that gives me data.

Have no codes.
Have good coolant temp... in fact 220+ with it 45-50 out.
Have VSS speed
Have good throttle position, MAF info.
Have good 4th gear switch on/off data.
Brake pedal switch works fine, passes current.
Fresh fluid & filter change. Old fluid wasn't abysmal in color/texture/odor.

Some hoser before me unplugged the TCC plug from the tranny but left it sitting up there loose, showing its weatherpak bellows. I checked it and its receiver with a mirror. Minor corrosion so I plugged and unplugged the thing a few times to scrape it cleaner.

My scan tool has a little LED that shows the computer commanding TCC-- it never does. I ran a toggle switch to ground the appropriate ALDL pin and it did actually engage once, but never again.

Head scratcher! Thoughts? Why would a bozo unplug the TCC plug for S&Gs?

It goes down the road good but without TCC it's putting a lot of heat in the radiator which makes it boil for a minute after shutting down.

TCC solenoid bad or TQ converter bad.

Ah, but why would the computer never electrically command it? And why would somebody unplug it? It's not like a 3t40 where it'd stall it out when stopping.

New solenoid fixed it-- with my toggle switch grounding the ALDL pin.

I'm going to say the old solenoid was flaky, drawing too much current, and burned out the computer output. For some reason it's not throwing a quad driver code. The scan tool LED runs off the ALDL connection and therefore was complicit in the odd diagnosis. Maybe some peckerhead mechanic climbed under there, unplugged the TCC to see if it made any difference, then shrugged and left it.

Plan is, I guess, to get a vacuum switch setup.

As for it running at 220, it still does that going 50 MPH down the highway (in glorious lockup!!!) on a 50 degree F night, but the rad fan pulls it down fast. I'm going to look into my air dams and see how many are missing and what sort of ram air I'm missing out on.