James you say air leak but don't the closed loop software adjust for this???
Reason i ask is i was trying to replicate a fault on mine L8 closed loop by creating a air leak to see if idle co would rise after taking dump vac off and boost gauge pipes off and adjusted idle to suit extra air the AFR still stayed around 14 to 15

I would presume that it would rise on a L1/L6 without closed loop control
was trying to create a fault a friends car could possibly have

Paul