Wavering idle after warm up

[FernsMJ]

Hello all! 
 

I’ve often lurked in these threads just looking for advice but I’d figure I’d just ask this time, as me and my Dad can’t seem to figure it out easily. 

 

My 4.0 92 MJ has a wavering idle once warm. After about 15 to 20 minutes of idle and messing with the throttle, the idle will begin to idle up to what sounds like 3k and drop down sounding like it’s about to stall. I can stop the fluctuations in the idle by unplugging the IAC valve but it continues once it’s plugged back in. 

I’ve checked my fuel pressure as I replaced it with an aftermarket rail and regulator and it sits at ~30 PSI and doesn’t change with the idle ideations.
I’ve replaced the IAC valve and the O2 sensor thinking they just “went bad” but I’ve had no change in the idle after warm up happened :/ 

I replaced the vacuum line from the intake manifold to the MAP sensor and my next theory is a bad MAP or a vacuum leak somewhere else. 
I have changed the intake manifold to the newer style and changed the Power steering pump to match, I’ve also replaced the throttle body to a machined aluminum and larger bore diameter. I’ve made other upgrades in other places like suspension but those are the only ones that feel relevant.

 

The symptoms initially began going down the road at highway speeds, it began to buck and almost cut out so I coasted to a turn out and shut it off 

 

I’d appreciate any recommendations or suggestions as I miss being able to take my beloved truck more than down the road and back. I’m stationed in Alaska so it might take a sec to implement anything that needs to get shipped.

 

Thank y’all for your time,

 

Fern and his MJ 

[FernsMJ]