Our 2015 X3 2.8d has been to the dealer 6 times in 3 months. Grunt. (under warranty)

CEL 1 - First they re calibrated something to do with a sensor in the exhaust.
CEL 2 - New sensor in the exhaust
CEL 3 - Another new sensor in the exhaust
CEL 4 - All new exhaust system and DPF

Latest check eng. light
CEL 5 - Vehicle failed high RPM airflow test so: Downstream Knock sensor and the swirl flaps need to be replaced and 10+ hours of walnut blasting in the intake.

^Anyone had similar issues? What on earth do swirl flaps do? Will a delete (EGR) reduce intake buildup? Is there even an EGR delete option?

Thanks,
Cam