Question on BMW 3-Series E36 O2_Sensor

Hi! Hope you can help me! I have a 92 325 with a 96 m52b28.i found out not to long ago, that I dont have the rear o2 sensor its been cut. i have 3 in total, is that 328 or 325 ? anyways, to the problem. When the engine gets to normal temprature, it get very bad preformance, and does not run as it should a all. It also backfires, and struggles to get rpm, like it is hasitating. Now i have read a bit online, and all the symptoms says that its an o2 sensor. But the engine was running fine when i bought it, no problem at all, but it didnt have the o2 sensor then, when i bought it either, so that causes me to think that it might be some thing else? And ye, why dont i just start by replacing the cut o2 sensor? Whell, there shoud be a conector on a bracket on the gear box ? Correct me if im wrong but thats not ther either, and i have looked to see if it was just tucked away somewhere, but i cant seem to find it. So then i have to lay up new wiring, and yes that is something i will do, but its not firs pri, and this is not my stronges side, if its not the o2 sensor. First pri is to get the engine to run properly. But if you could link me a wiring diagram, that would be great.
Wow that was a lot, hope you can help me, im pretty desperate, seeing that i need to have the working as soon as possible. Its my only car.

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[Nick at Pelican Parts]

A repair manual should have the wiring for your vehicle. I am not aware of any online diagram to link you to.

If the engine runs poor hot and backfires, fuel delivery, engine timing and exhaust back pressure.

- Nick