my ls in my 91 hatch back has had the o2 disconnected for about a yr now. so i finally decided to fix it and when i connect it the car runs badly. it stumbles and hesitates.. i tried 2 diff o2 sensors and the same problem . its like the timing gets way retarded when i drive , but if i unplug it the car runs great. so i left it off again.. but why would this be? , i even ran my own wire to the ecu pin c16 to test and it does the same thing.