When I turn my car on it vibrates - bad. It makes no difference whether it is idling, in town, highway, etc. It is also very loud. We have taken it to a couple of places and they replaced the engine mounts at one of them and we are told there is now nothing wrong with it. Driving or riding in it is like sitting in a very loud vibrating recliner. I am very frustrated - one mechanic even shook my husband's hand and said that there is nothing wrong with it and that he would have no problem with selling it as is. Every time we show it to someone they are very concerned about the vibration and noise. It seems the only people not concerned are our mechanics.
It shouldn't vibrate. However, many things can cause it. Has the vehicle been tuned up lately? Has anyone checked to see if the catalytic converter is plugging? Also, these vehicles are known to lose compression in one or more cylinders. Has that been checked?
Based on your description, it sounds like you have a dead miss. In other words, one of the cylinders isn't firing. I would suggest allowing another mechanic listen to it and let you know if that is what the problem is. A trained ear will pick up on that right away.