My truck does that too.It also will do it if it is idling for two minutes even if it is warm and the outside temp is around 20-23 degrees.

 

My 07 does that even when I'm plugged in. I was told that provision was built into the computer to cause high idle at a certain ambiant temp or if the truck idles a certain period of time. Dodge figures that the average owner will idle their vehicle and the upgrade is suppose to allow for less wear and tear on the pac.