Hi Nick, mine does this too but not as bad, I think its about 0.4 out. Like Big P said it's probably a ground issue unless you don't have the wideband output set right or the setting in MS right. I power mine from the Cig socket so I'm guessing that's why it's out a little. My first sensor just died giving an 04 pump cell error...I always forget to switch the thing on when I'm driving, I should really finish tuning the top areas of my fuel tables and take out the wideband. Are you going to take it to RWYB anytime soon?