v-10 idle issue

I have a 2001 F-450 super duty with the v-10 engine. I have noticed the idle jumping from normal (around 700-750 rpm's) up to around 1,000-1,200 rpm's for approx. 5-10 seconds and then returning to normal. It seems to do this after the engine heates up and a couple of times a minute. I have no trouble codes and have checked the coolant level and that apears to be fine. Any suggestions would be greatly appreciated.