Does this happen to anyone else?

I am not too terribly concerned about this but i am wondering if it's happening to anyone else. I have an 04 4.0L laredo with minor mods. When i've been driving long enough to get everything up to temp sometimes my idle at a light will drop to 500 rpm. with the exhaust i have on it sounds cool but it's still odd. oh and it went away when i filled up with a tank of 100% dyno fuel then started again with the ol 10% ethanol crap. I am just wondering what anyone may think this is and if it's happening to them. oh and i know it's not the trans cause you can put it into neutral and it still idles low.

Have you checked for fault codes? The IAC motor can cause idle problems.

no codes at all. i do want to get it on a better scanner and check the voltage readings but for the most part the thing runs fine and it just does this on and off when it wants to.