I can't figure it the fuck out

My 95 m series started to stumble and bog when accelerating. It's had a fluctuating idle for the month and a half I've owned it but, after an hour long round trip it stated sputtering like it's running on 3 cylinders. The only code I've had come back after clearing is the o2 sensor. I don't know fuck about obd1 and I'm skeptical just throwing a o2 sensor seeing as they're like 80 bucks for a Bosch and I just changed the cam angle senor that was a $200 parts cannon. Any suggestions? Throw a sensor at it and see what happens?