A 77 280Z would not have an O2 sensor. They didn't show up here until 79 when the 280ZX came out.

I have had a problem also, on my 72 240z my car idles at like 4000 rpm way way way to fast. I know i have the shitty carbs on it (webers) but i don't know how to adjust them yet! Could this possible not even be the carbs? if you have any tips please let me know! thanks guys.

this is definately a carb problem, I would find where they are adjustable and go from there. If the carbs are in good condition it should be an easy fix if they are worn it could be a vacuum leak