Shaking while idling

[kmammas]

My car is shaking while idling. Sometimes pretty violently. The mechanic first told me to do a tune up, change spark plugs, etc. When I picked up the car, he said it was still shaking and needed the motor mounts replaced. The car still shakes, but not as violently. He now said that the car needs new transmission mounts. Would the transmission mounts make the car vibrate while idling? I read different things on the internet. Some people say yes, while others say that the transmission mounts would make the car shake while driving, accelerating. Any advise?