Clio 197 O2 sensor 2 reads -100

Hi,
Just seeing if anyone can help with fixing an issue with my 197. It has an almost imperceptible (I'm undiagnosed OCD ;-)) loss of power at light throttle inputs. I've read all the posts re MAP sensors (I've cable tied mine) and after market exhausts requiring a re tune (mine is stock). I've recently changed plugs and coils and they helped but did not fix entirely. I used a scan tool and no error codes. The only evidence I have of something odd is the Bank 1 O2 sensor 2 short term fuel trim constantly reading -100%. The sensor voltage fluctuates but the reading is always -100% regardless of cold or hot running. Do I just change the sensor or is there something else that could be causing this? Is this likely to even be related to my power loss issue? Thanks for any input.