Just get the wideband installed already. Its going to take you about an hour to install it, just go do it. If the wideband also reads that lean, you've got a massive leak (doubt it) or a misfire (remember, fail to fire miss fires read lean on bosch lambda sensors because of how they function). Or if the wideband reads normal, the sensor and/or wiring like likely funked.
To answer the ecu question. You can have only certain circuits on an ecu fail, and you can have internal connection of the board fail over time from fatigue. Its really uncommon but it happens.