My '96 Cherokee has always had a small problem misfiring every once in a while but recently its gotten a lot worse. I had it read with a scanner and the code was P0135. Apparently its a bad O2 sensor. Just wanted to make sure, would something like that would cause the engine to misfire? If so, how should I go about my next step? Should I just replace all the O2 sensors and call it good? Also I noticed that the downstream sensor after the catalytic converter has the wires cut and wrapped up. I'm guessing the previous owner did this for some reason. I recently replaced the plugs, wires, cap and rotor, and the ignition coil as well so I'm pretty sure those wouldnt be causing this. Any help or input is appreciated. Thanks!

 

Definitely need those o2 sensors. Just replaced the ones on my '96.
upstream - NTK/NGK 23121
downstream - NTK/NGK 23014