well i got my car back from a shop today and the o2 sensor wasen't hooked up. it was running really poorly. what kind of damage could it have caused?
i was always under the impression that a car wouldn't run at all without an o2 sensor

 

Probably no damage. I would imagine with the o2 being out, the car squirts too much fuel causing the car to run rich. Hence running crappy. Plug it in, reset your ECU and go!