I would first make sure that the throttle plate stop screw is back completely away from the lever that holds the throttle open ever so slightly. Once it touches the lever only give it about a one eighth turn against the lever.

Then make sure the throttle switch clicks to close and clicks again when the throttle is opened let alone it being plugged up to the switch as another poster mentioned.

Another thing to check that there is some throttle cable slack over to the pulley from the bracket and that the cable to the firewall can wiggle with engine movement without affecting throttle.

I think you cleaned the bore of the throttle and possibly the flame trap air ways so things are breathing easier with more open passages.

I hope you tested the IAC with a nine or a twelve volt battery but this car uses a return spring IAC, so it should always close and idle low. THAT IS UNLESS, it is sticking or the computer does not know to make the car idle because the throttle switch is not closing to tell it to idle the engine correctly.

I do not own any automatics but the computer looks strictly at RPM being reported from the crank position sensor. I do not think there is any other sensor on the transmission that changes things unless there is a Park position circuit to the computer.

Some other Bricksters will have to chime in on that one!

Hope this give you some places to look! You have done a lot of good work and you just might be just slightly blinded by the gleem of happiness!

Phil