ASAP I will try to log and see myself what's going on my engine. According to what I read narrowbands, are working moving ECM to constantly supply the engine with alternatively leaner and reacher mixture as its signal is too easily running away abruptly from 0.45 V (14.7 AFR).
Yes thats how I understand them to work too. On mine looks like O2 target voltage is set to 0.493V and can be adjusted. Not 100% sure what you mean by "signal is too easily running away abruptly from 0.45 V ".
I am wondering if the up and down AFR is not the cause of the slightly fluctuating idle and the differences between engine pushes, almost cycle by cycle, when in closed loop. But, it is also true that narrowband is used almost everywhere and usually you can't feel any misfire or so...
Up and down AFR could be a symptom of fluctuating idle, however I doubt narrow band sensor is the cause of that.