While in park the car starts shaking, why?

jvaca0110

I have 2002 Jeep Liberty le. I turn on the car and after 5 minutes or so. The car starts shaking erradicatly. It only shakes while in park. But put it in drive or reverse no problem. Now the car was unused for almost 6 months. So it did have old gasoline but this morning 4/22/15 I added new gasoline. Is it the gasoline, is it a cylinder, is it a putting some Lucas oil, or some joints that are messed up, change the oil in the engine or transmission.  I want someone opinion before going to a mechanic. Thank you. God bless  

jvaca0110

Ask me anything that might help you have a better idea of this problem. Thanks again. 

elias

motor mounts.