Intermittent stumbling idle issue, 1996 4.0 AW-4

So I've searched on & off for a few days with not much luck in finding a similar issue.
So recently past 6 or 8 mons. I've been experiencing intermittent idle issues where if I'm sitting at a stop light or poking along on a trail or idling while airing up the XJ starts to 'load up/or starve'... the idle will start at 800/900 RPM & slowly start to get lower & start to run rough, sometimes I can hop in it & gently feather the throttle and get the RPMs to rise then say above 2500 RPM it'll smooth out and I can bleep the throttle to blow it out... sometimes it'll stumble & struggle to stay running... hence the need to 'feather' it.
It's very random, one ride to work might be fine or a longer trail ride it might happen multiple times, distance doesn't matter. I can get on the freeway & it'll run like a scalded cat ! A couple times that I've 'cleaned it out or blew it out' I got a sulfur smell... it's not like there is a lag on acceleration it just won't go... then I 'feather it" and it'll slowly get going, frustrating at a stop light...
The XJ has about 165K on it & I had the head rebuilt about 10K to 14K miles (about 2.5 yrs. ago) ago replacing the cap, rotor, plugs, wires & such. The Cat. is a Magnaflow replaced approx. 50K ago... there is no rattling.
After the latest time it threw some fuel codes... Random mis-fire & cylinders 1,3 & 4 misfire...
The fuels system is unmolested so far... it'll pressure up in a second or two..
Just the other day I checked fuel press. and it was at between 46 & 48 psi idling with no hint of it loading up. There was a flutter on the gauge needle as mentioned, maybe the gauge isn't the best of quality or the psi was truly fluctuating a bit ?? I was hoping it would act up while the gauge was on it.
I'd really just prefer the damn thing fail so I could figure it out and not have some random idling issue...
-It'll start pretty quickly...
-Semi-new cap & rotor, plugs & wires...
-Magnaflow Cat. with approx. 50K on it...
-Rebuilt head & such 10K to 14K ago...
-O.E. fuel pump...

I just don't know to look to the fuel side or the ignition side... OR ! a sensor somewhere...
OH !! one other random odd idle issue is on occasion it wants to idle say in park at 1500 RPM... I bleep the throttle & it returns to the 800/900 range.
Sorry for the length I just wanted to paint as clear of a picture as I could...
As always any thoughts or advice is appreciated... while I'm OK with a wrench I'm by nooo means a mechanic...

Thanks...
Curt

1st thing - Check for Exhaust Leaks. '96 Models Are Real Finicky about Exhaust Leaks. Trust Me. I Just went thru that Problem w/ mine.
2nd - Clean or Replace the Idle Air Control/Stepper Motor
& Clean the Throttle Body.
3rd - Check for Vacuum Leaks. Check Vac Lines @ Intake Manifold.
(Hose Clamps Work Great for this)
From my Experience (Been Driving My '96 for 6yrs) it's Probably the IAC &/or Dirty Throttle Body. 2nd Guess would be Exhaust Leak.
UncleSarge58

If I was throwing money at it, I'd start at the fuel pump.

I would make sure all the manifold bolts are tight. The way you need to feather the throttle, makes me think the TPS could be the problem. When the Throttle Position Sensor (TPS) starts going out it can cause weird problems. On mine, it first was noticed causing the engine to rev UP (like a downshift) when taking my foot off the gas to decelerate and exit off the highway (TPS also is an input to the TCU). It caused my idle to go up to 2000RPM when I first started it and the engine was stepping it down 500RPM at a time to get back to normal idle. It also caused some very brief cutouts in engine power with steady throttle cruising down the highway. All of these things occurred within about a week and half, but not everyday. After the cutting out on the interstate, I bought a replacement on the way home from work (dealer stocks it) and have not had any of these problems since. It can be hard to diagnose because they can fail hot when we aren't as likely to try and test it. It is also a good idea to check the Idle Air Controller (IAC) and vacuum lines as others have said. From what I have seen and heard the IAC rarely fails such that it needs to be replaced. The TPS cannot be cleaned or serviced. I am not sure that the crankshaft position sensor would be a culprit here. Whatever sensors you buy, I would go straight to the dealer.

Thanks guys I'll be looking into the above mentioned items...

TONE !!! the only thing you throw $ at is food... and maybe beer... :looser:

Curt

Pretty much just food... YOLO