I was checking a friend's car with my wideband, and under load it had a miss and was running on the lean side for WOT. I replaced a bad plug wire and the miss is gone, but I was not able to check it on the wideband afterwards. Can a miss like that (unburned fuel I am sure) show up as lean?

 

Yes, it will show lean but not due to unburned fuel but unburned oxygen. Remeber a wide band is measuring with a Oxygen sensor that could care less about fuel.

A miss will always show as lean(excess oxygen).