That actually sounds like normal behaviour. The processor should ramp up and down as it does the tasks the OS asks of it. Idle is never really idle, there are always things going on in the background...and when these processes require it the CPU boosts and then idles again.
Maybe you have set a balanced power plan instead of Performance something like that? Performance often pegs the processor to a high constant clock speed even though the CPU should be at idle. Balanced (or editing the performance power plan minimum processor speed) allows the CPU to manage itself...the Sense MI magic!
