Question would a bad oxygen sensor cause poping

Year make and model of your vehicle would help alot. A o2 sensor that is bad and reading lean all of the time will foul the plugs out, and make the vehicle run rich, so will a bad coolant temp sensor. The popping sounds like you didnt get the firing order correct, or the timing is too far advanced.

Along with what btemple suggested I would add that oil fouled spark plugs could be bad rings, a leaking intake manifold gasket that is sucking oil out of the valley if it's a v-6 or v-8, a problem with the PCV (crankcase ventilation) system (look for oil in the pcv hose there should be none) or a bad valve guide or valve guide seals. The popping could also be a bad valve. I would suspect that since two of the symptoms point to the valves. Is it just one cylinder fouling the plug or all of them? Does the engine smoke? and what color is the smoke? Black smoke is an indication of a rich condition like btemple is describing, Blue smoke is from oil, and white smoke is antifreeze.

If it's running rich, the fuel could be getting into the oil which would bypass the piston rings and foul the plugs. That would also make the popping sound from the exhaust pipe.

Flat cam