You maybe looking at this from the wrong end if there is an eng. misfire unburned fuel charge and unburned o2 are sent down stream the o2 sensor sees this o2 as a lean condition and tries to correct the a/f mixture the thing I would do is check compression to eliminate a mechanical misfire like valve too tight flat cam broken piston ring then be sure there is not an ign. misfire like spark plug, plug wire, dist. cap rotor or coil diagnose the problem so you not running around chasing your tail ok that's my 2¢ worth ......ted