Geizhals

So out of no where i noticed when in nuetral my rpm is going from 900~ to 1500~ and back down and back up 3-4 times, then equals out. Doesnt matter if i am in nuetral or 6th, it does it. I cleaned the throttle body about 600 miles ago and it didnt do it then, i checked today and it had some carbon, so i cleaned again(car on(not running), pedal down to open the valve). I am not sure what is going on. Thanks