I think my car is possessed, so far this used to happen every once in a while but it is happening more often,

When i first dirve the car it runs fine but on my way to work something weird happens, it seems to be reving high, what i mean is, if im in traffic or even driving on the highway and i put the car in nutrual it revs at 2500 rpm, now it dont happen when i start the car and even tapping on the gass dont bring it down, now heres the wierd part , when i get off the highway about 40 minutes later and get to my fist light i put it in nutral and it revs at 2500 for a few seconds and starts to go down on its own,.

Any ideas what is causing this?

adam