...what could one expect, as far as noise, vibrations, or whatnot, if one of the 4 motor mounts on a 96 toyota corolla sedan were broken?

I took the car into a local Toyota dealership and they told me it was an engine mount that was causing the vibration on acceleration on flat pavement. The vibration only occurs in the front left wheel and it feels as though the tire is very badly balanced (but it IS balanced). I'm not sold on their answer and thought I would check in with you guys to see what your thoughts might be.

Any help is much appreciated.