Hello, my name is Idle Stumble

[samrebel]

Sorry for the stupid title, but I need some attention. I have a slight stumble in my 96 XLT 4.0 with 115,000 mi. Its not a rough idle, but more like its vibrating at a very small amplitude, then every few seconds, much larger jumps for a second, then back to normal. I've replaced plugs (except for passenger side rear, it was too hard to get to) wires (ditto on passenger side) IAC (it was howling, cleaning didn't work) cleaned MAF, even tightened air cleaner hoses. The truck runs great otherwise, accelerates good, OK gas mileage, etc. Sometimes the stumble is more noticeable than other times, I haven't been able to link that to any certain situation. I know a lot about engines, especially fuel injection, so if you've got to get technical, lay it on me. I haven't gotten to compression checks, manifold leaks, etc. yet, I want to try easier stuff first.
Anybody got an idea?

 

[performancenut]

Carefully scrutinize the vacuum lines. A vacuum leak is a common cause with inexpensive repair.