I dunno what you mean by an a/f ratio gauge... If it is really running lean, then the O2 sensor is doing the right thing and alerting the PCM. Could be an air leak somewhere on the intake for the front bank?
I dealt with the 176 on my car about a month ago. O2 sensor fixed it, but if the code had come back I would've been thinking air leak (that's what others here told me could give me a lean mixture on one bank).
Good luck.
Brent
