Q: O2 sensor causing misfire.

Hello. If you have a misfire, most of the time that will set a misfire code. If the only code that comes up is an O2 sensor code then you may have a bad oxygen sensor or you might have a fuel mixture problem. The most common cause of a misfire that I have seen on this engine is a bad valve seat. Most of the time this will set a misfire code for that particular cylinder, but not always. What a mechanic would do to diagnose this would be to install a computer scan tool to see what the O2 sensors are reading. If the voltage of the sensor is not fluctuating then the sensor may be bad. If it is then they would check the fuel trim readings to see if there is a fuel mixture problem. I would enlist the help of a certified mechanic that has a scan tool and knows how to read this data, like one from YourMechanic.