01 Pathfinder - P0140 O2 Sensor Circuit No Activity.. Could I have fudged it?

[longhornsqx4]

Well about a week ago I pulled my stock intake off the car, and added a aftermarket piece, stock maf sensor location etc, but i disconnected my battery overnight, connected it in the morning and when I went to start the car is sounded like it was running on 3 cylinders it was so rough. It ate gas all week and sucked on cold startups but once warmed up would run better, it would also sometimes die at stoplights.

Well my car finally through a code today after about 50km of driving in this s***ty condition.

P0140 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

Its been running like crap, running rich and idling bad and sucking down gas. Do I need an 02 sensor or could something else be at fault here?? I erased the code with the scanner but it seems to be running the same

When it says bank 1 sensor 2, which one is that?? Kinda confused on that part. And if I should just fix the 02, or a cheap aftermarket replacement??

Any help appreciated

[longhornsqx4]

I disconnected the battery again and let it sit overnight, connected it this morning, startup was a little rough and had to give it some gas to keep it alive for a second, then it levlled out @ 1200rpm (its cold as hell), idled DECENT for a few minutes without stalling, but still sounded rough / small miss

No codes popped up right away, but I didnt go anywhere and drive it any place, had knowwhere to go lol