So i installed a brand new AEM UEGO wideband about 2 months ago on my Evo9 MR. Since the day i installed it my AFR at idle always read 16-18, at the time i figured it was the tune and didnt pay much attention to it because of that and since it was only at idle and not WOT. This was on stock inj w/ walbro 255 and just a quick little reflash tune btw.

Fast forward today as im trying to get tuned by Tom aka TSCOMPUSA (whos been nothing but overly helpful on helping me diagnose the problem) i noticed that even on perfectly stoich fuel trims at idle, my wideband is still reading lean in the 16-18 range. Another sympton iv noticed is that now after installing the 1250cc inj when the car idles lean (like it always has since the wideband was put on) it now idles rough and is jerky sometimes part throttle. I know its not the tune since my trims are good and front o2 feedback is good aswell, so that leaves me to think that something is causing my wideband to show lean AFR (when its really not) which in return gives me rough idle while idling.

What do you guys think the problem could be? Boost leak, Exhaust leak, Vaccum leak, something fuel related? All help is appreciated, Thank

P.S. sorry for the long paragraphs lol