so far this is the hardest to diagnose problem through thread searching, most threads never reached a solution with this code since it could be just about any sensor on the car on top of fuel system problems.

the issue I'm having is that the car wont go into gear without stalling, I need to be actively feathering the throttle for it to not stall.
I have erratic idle +/- 500rpm.

most important of my observations has been this: a code is thrown almost instantly on a cold start.
ALSO, it doesn't want to idle cold. another issue where I have to feather the throttle.

any other experience, or things I should try out?

The ECM will set code 45 when the ECM detects a high voltage from the oxygen sensor, throttle is applied and the system is operating in Closed Loop (conditions must exist for longer than 50 seconds and engine must be running for at least 1 minute).

But you said your car threw the code right at startup?

What year and engine/trans?

2.8L V6 A/T
I jumped the a/b diagnostic terminals when cold to reset the IAC, and then I unplugged it.

so far no code... weird?

okay, so I swapped out the IAC with a new one, and the erratic idle went away and so did the persistent code, so far so good.

the code for rich exhaust still pops up once in a while, so its probably either the regulator or the injectors with the fuel.

I know a lot of things could cause the rich code, but what are the most common?