AE86 Oxygen Sensor help...

[NoHachi]

The freedom ecu does run closed loop during most circumstances, so the stock O2 should be plugged in...

The more I read about all these little things that are wrong with your car, the more I am convinced that you are one lucky bastard. The engine could have blown any time if even the ecu has no clue as to what the AFR is.
The only thing i can come up with is that someone tuned this thing for the track. That would mean running it in TPS mode, which is not really suited for closed loop operation. That would also mean that you should at least have to upload a MAP basemap before you can start running closed loop. Any way in which you can check the mode the ECU is running in?

I would check these things first. It could be a matter of just plugging the sensor in, but might as well make sure.