Mlambrix84

Hi fellas, I have one that is driving me nutty. 07 auto 4.2l. with 104k .
Truck drives great with good acceleration and fuel mileage. Fuel trims are spot on (+/- 5%)while driving but once idling short terms slowly move to 53.1% and long terms go to 29.7%, it then throws lean codes on both banks and dies or stumbles and dies. I smoke tested for vacuum leaks and the smoke would eventually come out of the egr. Replaced egr and no change. Any help would be appreciated.

manicmechanic007

Major vacuum leak
The intake manifold gasket and the isolator bolts
Replace them and retest the fuel trims

manicmechanic007

Those lower plenum intake bolts with the rubber washers are what they are calling isolator bolts
Reason unknown like the compliance bushings

Johnny Paycheck

Manic, you sure about that isolator bolt deal being valid on this body style 4.2?

I’m pretty sure the intake changed between generations to where this wasn’t “a thing” on ‘05-later engines.

OP has a leak, but I haven’t seen an 11th Gen 4.2 recently to recall the quirks it has.