Why does my vehicle shake while in park?

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. Ask me anything.  Thank you. God bless  

elias

Add a bottle of "dry-gas" to the gas tank.
Inspect motor mounts. (Watch with hood up: does engine "jump" when you put it from neutral to drive/reverse?)