O2 sensor is gone, replace it. had a P0171 on my mothers car and replacing the noted sensor for that code cleared it up

if there was a intake leak or something like that both banks would be lean

- 95 Mystique LS - Zetec/5spd - 99 Contour SeVT Sport - Duratec/5spd Official NE-CEG Contour/Mustang Family