1999 Jeep Cherokee Shuttering

I have a 1999 Jeep Cherokee that my office uses on a daily basis. The vehicle shutters while at an idle, almost like a miss. If you give it some fuel it will stop doing it. However, it seems to only do it after it has been running long enough to be warm. We have changed the plugs, wires, cap, and rotor button. Do you guys have any ideas?

Thanks for any help you can give me!
B.P.