It's probably an ignition issue. Try swapping an ignitor with a buddy and see if that works. Also, what are you gaping the plugs to and what kind of coils are you running? Pull the cover off an pull the coil plugs off one at a time. the one that doesn't just about kill the motor and sounds the same is your problem cylinder.
Your car probably isn't actually running lean. If you don't have spark in one cylinder then air and fuel is just passing threw causing the wideband to read lean.
Hope that helps.