Finally got past all those misfire codes and got the car registered. Drove it to work yesterday and everything seemed fine. On the way home I stopped to fill it up and shortly after the check engine light came on. Was hoping it was going to be the gas cap but pulled P0134 for no activity on primary O2 sensor. Surprised the reading would be inactivity since the car seems to drive fine. Any ideas on what to check out? Previous owner never had CEL so this is new.