Check eng light on codes p0171 and p0174 what do i need to change
If you do not find an obvious problem in the vacuum hoses or PCV connection, I would sadly suggest you prepare yourself for a new lower intake manifold gasket. Those two codes combined indicate that the leak is not in one spot, but across the rear of the intake. This 4.2 V6 is known for this failure, and many TSB's have been issued regarding it. If you don't want to spend hundreds replacing sensors and getting your ECM rebuilt just to have a truck you cannot get inspected, spend the $90 for a smoke test on the vacuum system. I wish I had done that two weeks ago. I will be changing the gasket this weekend.
Intake leaks can cause this code set
Sorry it took so long to update my answer, but I have since discovered that the MAF sensor I bought went bad in less than 8 months. Of course I didn't expect that to happen, so I KNEW it HAD to be something else. So after changing the intake gaskets, isolator bolts and grommet, and IMRC bushings, I started putting the old parts back on... and MAF sensor wad faulty.
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I would check the pcv tube elbows, very common for deteriorating and causing lean codes.
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look for vaccumn leaks
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