That was my thoughts bnmccoy. If it isn't MAF then it is EGR. I think they said something about 45% -50% being the max closed on the new duramax if I recall correctly. They also said something about it increases the EGT's and it helps to warm up the motor when it is cold out. Fast heat in the cab I guess.

I still don't like the idea of soot being sucked back into the motor.

 

you cant access much of 08's engine without removing the cab, according to the mechanics at my local ford pickup dealership.

 

i'm pretty sure that my '02 excursion does some sort of exhaust cutoff thing, when it's cold out, since day 1, you could always kinda just hear that it wasn't letting much exhaust out, that thiing warms up so much faster than a gas engine though! so whatever it is, it works!