*probably* just a dud sensor or a bad connection somewhere.
Are you tuned? I can't really recommend having an MBC, but if you're satisfied with the results, and your turbo is happy and everything, you may just want to adjust the fuel map a little and definitely disable that DTC.
It's a 2002 wrx with 148k miles. I have a vf39, sti pinks, 255 pump, catless uppipe/turboback. And yes I am tuned, at 15psi. I have a hallman mbc.
It runs great, no problems whatsoever. The sensor has only been installed for about 10k miles. I checked the connections and all seemed fine. I ordered a sensor today; so i will go from there. It is acting similar to the video that Donkey posted.I will have my tuner double check the tune for safe measure.