the 4.0 doesn't have VCT so I don't see what a tune would do.

 

Just because there is no VCT doesn't mean the timing can't be advanced.
If a loppy idle is what you want you'll need to swap cams.

 

Know where I can find some for the 4.0?

 

The 4.0l is quiet at idle. I've heard many different exhaust videos, and these engines just aren't that loud at idle. A mod that would make this engine loud at idle would likely make it unbearable with any acceleration.

Swapping cams (big $$$) likely won't make the idle much louder, neither will a tune. The only reasonable thing I could think of would be to raise the idle a few hundred rpm with a handheld. I've noticed when the engine's racing from a cold start the exhaust is noticeably louder then it quiets way down when it settles to idle.