As mentioned, the Idle is an 'Open Loop' affair in the 300. so the O2's are ignored at idle.. once the Idle Mode is entered, as seen by the 15 Deg Ignition Advance and 700ish RPM .. I have Widebands on one of my NA's, and I always see Left bank at about 14.5/15 and right bank at 16/17 AFR's at warm idle.. Not sure how the Cars pass smog this way, but this one did it with flying colors..