Well, I have an update.
First off, I've cast the theory of the failing TPS out.
First, let me state that it will run holding down the gas slightly, but after warming up a bit it will idle at around 600rpm, with the A/C on.
I read through the part of the Haynes manual dealing with emission controls and such when it hit me: I haven't hooked up the exhaust pipes yet! The CPU is adjusting based on readings from the O2 sensor(s) which are not reading correctly, this could be my whole problem with the idle. I'll let everyone know when I get the pipes hooked up. I didn't hook them up yet because it looked like a rat had made a rat's nest in the 'Y' crossover part (it has been sitting since '07), so I wanted to take it to a muffler shop to be safe before I hooked them up. Or, at the very least, get a good shop vacuum with the long flex tube and clean it out myself.
Questions, comments, or advice are welcome.