Engine Shakes

My 2000 Eclipse GT has been sitting in storage for about a month. Yesterday I decided to take it out for a ride. I noticed that when I turned the ignition off the engine shakes. Does anybody have a clue as to what it could be and thoughts and ideas on the topic would be greatly appreciated.

motor mount? might one be broken or torn...

other than that... not much causes vibration unless it something is out of balance

How high were your RPM's when you shut off the engine. If your car is reving when you shut it off the engine will shutter, or if your idle was a little high it will do this. If your car hadnt been driven in a while it may have been ideling high simply because it was getting used to running again. Make sure you put a fuel stabilizer in if you plan on storing for a while, or you will run into some engine problems associated with bad gas. Other than that, and what Elchico said, idk