[mark houghton]

It aint the sensor, as you've already discovered with the new replacement making no difference. My guess would be your control pressures are off; WUR issues, one pump or the other not working right, system pressure too low. You should not be running 12.1 or 12.5 to 1 AFR at idle. You could probably adjust it out with the mixture screw, but that doesn't fix the root of the issue.

The other possibility is that your AFR gauge and/or sensor is faulty and feeding you bad information. I had an issue once when my voltage regulator in the alternator was going tits up, and after warmed up (following a short shutdown to heat sink things) my AFR's would suddenly be in the low 12's just driving around normal-like. I was way over charging the battery and causing some funky issues with the Innovate AFR circuits.