Alrighty folks, I think this might be a wrap. Since I've literally tried EVERYTHING... I decided to finally adjust the butterfly stop screw, and it brought the idle down!!! I guess the thing was just taking in too much air through the butterfly?
I took my original throttle body, I shined a light through it and re-centered the butterfly with a feeler gauge. I kept shining the light and closed the butterfly as much as I could with the throttle stop screw and brought it back out a little. Instead of having a .003" gap l, I brought it down to maybe roughly .0015" or .002".
Was adjusting the stop screw the correct thing to do? Maybe.. I've tried just about everything. IAC, TPS, intake gasket, a different TB, all my vacuum lines, deleted C101, fixed sensor grounds, smoke tested by myself and a shop, replaced the EGR, MAP sensor, MAP sensor line, O2 sensor, ECU, and probably a lot more. I probably need to touch the 'adjustment' up a bit more, likely the idle bleed screw, but it's much better. There still seems to be a 100-150rpm-ish difference between P/N and gear, but good enough I suppose.
Unfortunately for the crazy part. When driving it the other night. I braked pretty hard for a stop, and I heard what sounded like a bag of rocks under me. Turns out my NP242 transfer case took a dump.. What good timing.. I'll be having it repaired. I don't think the transfer case was taken care of that well, when I did the fluid last year, only about a quart of old black oil came out. It's possibly never been done before. When I inherited it, I was also told that supposedly the 4wd didn't work. So there's that.. All the chickens coming home to roost.
