2011 Traverse 203000km

Lone p0420 code.

Engine runs at 12 to 15% at idle. Ltft normalizes off idle. No vaccuum leaks found. Fuel injector/system cleaners used to no avail. Stft oscillate between -3 to -7 on idle.

A few weeks ago when temperatures were above 18C, ltft were 5 to 9 per cent.

When it got cold (4 C), that's when the ltfts were at 12 to 15%

I replaced the purge valve solenoid, pcv valves, a pcv valve hose that had a bad o ring. I recently cleaned the throttle body and maf sensor. TB gasket replaced. LTFT values didn't get better.

Oxygen sensor 2 follows Oxygen sensor 1 when graphed.

I may have found an exhaust leak at the seam of the resonator or muffler (not sure which). I've put exhaust putty on it. Don't think it was the weep hole.

Vehicle had a history of exhaust leaks that's been repaired per the service records (carfax records)

The car runs fine. No drivability issues. But the high ltft at idle is concerning to me.

I hope all the info provided are relevant.