Doqui

Hi , I am a recent 2003 Micra owner which I really like driving. It goes and sounds nice but always after 10 to 15 mins of driving it from start it has a weird minute or so where the engine loses power intermittently and gets a little jumpy. It doesn't last long and it seems to sort itself out and then runs fine . The engine light is on and shows O2 sensor codes. I have replaced the downstream sensor but still no change. Anyone got any ideas before I change the other O2 sensor?