So I noticed this problem when tuning, it makes things very frustrating.
I start tuning after the car is warmed up. Set the idle, sitting right where I want it at 14afr. However after driving for a while I stop and the idle is in the low 13s / high 12s. So i corrected it back to 14. Shut the car off for a bit and when I fired it back up again the afrs are >16!
This all occurred when the coolant is at operating temperature, so WUE is not a concern.
What could be causing this? Im thinking potentially heat soak from the MAT sensor? But i have MAT correction turned off. I noticed the hose from the oil filler to the intake is collapsed, maybe this is another cause?