well it was running great for the last few days, but today it was worse than ever, the oxygen sensor light was almost always on and it stalled on me once going about 10mph.

I just dont know what else to change, what would be the next few things i should replace to get it running right?

car has 114,000mi
idle is nice and steady at about 600-700rpms untill the o2light comes on then it will drop down and then jump up to 1000rpms.