vibrates or shakes

I have a 2007 CRV LX. When I start it up its around 2000rpm and then as it warms up the rpm start to drop. At 1100 to 1300 rpm it shakes the entire car (I feel it on the steering wheel and the seat). I can replicate the vibration by reving it up to the 1200rpm range at idle (P or N). My car has...