my 08 se 4.0 has done this since we got it. Dealer said it was a bad motor mount, so i installed two new ones and the problem didn't go away.
Granted I installed some cheaper aftermarket ones, but you would still think it should have fixed the problem. It happens at stop lights, idle drops to 500 and shakes the whole damn car. It's annoying, dealt with it for 50k miles and now that we want to sell it we need to fix it.
I guess I'll get new motor mounts, and transmission mount and see if it helps.
I assume cleaning the idle air control valve would also help maybe?