Help! Might have bought a lemon?

Why don't you follow the methodology in the work-ups that SFO posted in post #4?

 

Mice love to eat wire insulation on these cars. It's veritable pop-corn for them. They mostly congregate behind the glove box in the air filter area. If I am not mistaken, that may also be the location of one of the ECUs. Don't quote me on it. Do check out the state of your cabin air filter. If you have or had rodent infestation, that will have evidence. If mice have been in the car, expect some strange electric problems.

Not sure how to help you go about finding the problem, but just knowing if it was rodent damage can point you towards a more likely area of damage.

 

Well, the first of the two workups posted in #4 doesn't even have much methodology to offer, other than to try replacing the throttle body, which happened back in #31, so it's safe to call that first one 'followed'.

The second one does offer a bunch more information, and some hints at distinguishing the remaining possibilities of wiring/connector issues or ECM issues, and that's pretty much where OP's focus is now, so some rough methodology-following seems to be happening.