Ok I am new here so try to be patient with me.
I have a 98 Ford Ranger 4X4 4.0 with 146K miles on it. Overall the truck still runs great but about a month ago the check engine light came on and can not find the source of the problem. Lean on both banks and everything points to a vacuum leak. These are the things that I have done so far:
1) Changed all three O2 sensors, (then found out that this would not be the issue)
2) Cleaned the MAF sensor
3) Used starting fluid to spray around the intake as well as all of the vacuum hoses.
I am sure that performing a smoke test would be more accurate but have not found a place to rent one, buying one for a $1000 bucks is not an option.

I could really use some help here

 

DO a search should be a ton of info on it.. Idle air control, mass air would be common causes.

 

I'm a noob with a new to me old 2.3L 4 banger. Not long ago I cleared up code 174 by correcting vac leaks associated with my "intake manifold runner control" solenoid (IMRC) and the related "swirl control valve" (aka actuator). I'm sure you've read a long list of things that might be causing it so maybe this is useful maybe not. Besides.... I don't know enough about this to know if your rig has similar components, but if this is your problem too learn from my mistake..... I thought the solenoids two vac hose nipples were bidirectional but they're not. Anyway code 174 gone, and it drives smooth. But I still have code 171.

Also, I just made a smoker for no money at all. Look for "shopemade engine smoker" on youtube. I just used a cardboard coffee can and lid, with a couple extra air compressor fitting hot glued in. One fitting gets a hose to run to engine. Other is for applying a bit of air. No air compressor? Just breathe into a bit of clean tubing. For smoke, I used cone incense on a cut down soup can to serve as a burning tray. The cut down can has some holes drilled for good air flow. Piece of scrap wood on the burning tray lets me light the incense then lower the burning tray into the (coffee can). Put on lid, and apply air! Works great. Cost zero, given the bit of tubing and fittings already in my garage.