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I did pull the entire PCV tubing assy. Tubes are all good, only small surface cracks on the boot that connects to the valve.
Single digits out there right now, so not too interested in working on this problem today. It's supposed to warm up starting tomorrow. Will continue checking per your suggestions then and post back later in the week.
not sure if it is the same on your year of truck, but on the back of the engine there are two vacuum connections. The one on the left goes to the brake booster and the one on the right goes to the 4x4 actuators or something. Possibly one is cracked or loose. Difficult to get at either way.
Hook up your scanner and monitor the short term fuel trims. Hit suspect areas with your flammable spray, I usually use brake parts cleaner since I usually have it on hand, and watch those trims. When the extra fuel is sucked in, you'll see a distinct change in the STFTs.
Tried that watching my STFTs. Found a vacuum leak at the bottom of the white hose pictured below. Had to post a pic because I don't know what it is!!☺️
Did it fix the problem? No, but it's better. LTFT on bank one is acceptable just under ten, but bank two is still too high. I hit around the COPs on bank two and around cylinder six the STFT drops way down and the engine stumbles when I spray carb cleaner around it. Must be some kind of gasket or plenum leak I suppose. Hard to see. Anyway I made progress, so thanks again for the pointers.
My truck 4.2L v6 had these codes P0171& P0174 and replaced the plenum gasket, isolator bolts and cleaned the lower intake in which was fill up with carbon deposits and gunk. 5 years and still no problem
