I have a 96 Civic d15b non-vtec swap with a p2e-a02 ecu. Car runs and idles fine but I’m throwing a code for the o2 sensor. However once I swapped the new sensor on, the car idles around 1400, drops to 1000, then shoots back up to 1400 and so on.

Should I just keep running the bad sensor? Why would it idle worse with a new one?

IACV has been replaced and as far as I know there are no vacuum leaks.

Any help is very much appreciated.