I was getting the lean code P0171 Bank one (2.5L) I found 2 very small holes in the line that goes to the vacuum storage ball. Fixed those. No more CEL. I checked all other lines and zero leaks. Sprayed 2 cans carb cleaner and nothing. Next thing is smoke test but this issue seems to have started from one day to the next. I have attached some screen shots from my OBDII scanner.
The truck runs beautiful just off idle when I drive it and I still get about 20mpg. When I come to a stop it idles horrible and will sometimes almost die. My STFT maxes out at 42.19% at idle so it looks like I still have a vacuum leak. Fuel filter has less than 10k miles. Injectors are new. Plugs, wires, and one coil is new. Timing belt is new. (I did the head gasket April of this year and put all new parts on it)
If I unplug IAC the idle drops. (IAC is about 1 year old) Unplug the MAF and idle changes up and down for a little bit and then it dies. (No CEL though) MAF is about 3 years old.
Besides doing the smoke test I'm at a loss as to where to look now. Sometimes it goes into Open Loop even after I have driven it for several miles and it is fully up to temp.

 

Misfires cause Lean codes and high STFT

Easiest way to check for vacuum leak is to warm up the engine then, while engine is idling(800rpm), unplug the IAC valve
If RPMs drop or engine stalls then no vacuum leak
If RPMs do not change then you have a small leak, but not enough for STFT above +20

STFT should go Rich(+ 10 STFT) at idle that prevents engine from overheating

Is your speedometer not working?
Computer is showing 0 MPH, so you should get P0500 code

You can unplug the 3 wire connector on a coil pack and start and run the engine on just 4 spark plugs, ran that way from 1974 to 1988
This will test if all 4 spark plugs on that side are working, if you have a steady misfire then at least one spark plugs is not working
Then test other coil pack the same way

Engine will have less power on just 4 spark plugs, thats the point of having 8, better power

Manual or automatic trans?

 

Automatic trans
The speedometer does work it just doesn't show it on the OBDII.
I unplug the IAC and it does drop in PRM. ( a couple times it stayed the same but the idle was already about 600)
It sounds like a bad misfire at idle but right above idle it runs perfect. I'll try to unplug the coils one at a time. I do have one OEM coil and one aftermarket.
The STFT is ALWAYS 42.19 at idle now. It was not like that before this happened.

 

Pull out PCV valve and put a piece of tape over its end or remove it from its hose and plug the hose, and start engine

PCV valve should be closed at idle if its sticking open that would be a "vacuum leak" and cause the higher fuel trims
Also check the Breather hose, make sure its clean and not clogged, if it gets clogged up "blow-by" can push PCV Valve open at idle
Blow into the Breather hose to make sure it not clogged inside the valve cover

Dirty MAF sensor can cause high STFT at idle as well, but work fine with higher air flow

 

I didn't think about PCV. I'll try that also.
I did clean the MAF with MAF cleaner. Not that it can't be the issue but at least it's clean! LOL
Breather hose is good. I replaced it when I did the head gasket because it was showing signs of dry rotting / cracking.
I'll be working on this tomorrow so I'm open to any other suggestions to try!

 

So an UPDATE
The IAC was cleaned but didn't really need it and the idle does drop when unplugged unless it's already really low.
Using carb cleaner again I finally found that the idle increases when I spray it under the throttle body. I replaced the TB gasket, the small hose that connects to the metal pipe that goes to something on the driver fender well (I'm not sure what it is! LOL) The hose for the PCV. The PCV is not stuck either. I tried to snug up the lower intake bolts and only one needed a small turn. The upper intake bolts were all tight. After all this I still get the idle to increase when I spray carb cleaner under the throttle body!!
I guess I will have to try the smoke test next.

 

The hose on the underside the throttle body goes to the EVAP canister, sucks fumes out of the gas tank thru the charcoal filter in canister
Its a Ported vacuum, so only has "vacuum" when throttle plate is open

 

Thanks Ron for that info!
Hopefully the smoke test will show me the real issue.

 

Might want to check fuel pressure if at all possible, low or unsteady fuel pressure can also cause lean codes.

 

UPDATE
.
It was the gasket from lower intake to cylinder head! Replaced gaskets and cleaned everything up and now back to normal.

 

Good stuff

Thanks for the update and THE FIX

 

How did you find out that the gaskets were the problem? I'm dealing with the same issue, my ranger can't run over 60mph @2000 RPM at 4th speed, as well as the AC is not blowing into the cabinet.