o2 sensor help

I recently had an o2 sensor problem in my 91 hb and I had to add another bung on the manifold which I got done today, and then I had to hook up the o2 sensor which I also did, but the car still runs boggy for some reason and it STILL flashes 1 red light when I turn on the car.. I'm pretty sure it means o2 sensor. The ecu is a pr3 obd0 and my motor is a b16a. I'm not sure whats up with it.. any ideas??