My 93 4dr does it too, worse with the a/c on, but I know that my two lower motor mounts rubber centers are dry rotted, and they need to be replaced, motor mounts will generally do more than just vibrate only at idle though, for example on mine, you can feel the engine rock slightly when you get on and off the throttle, and when you shift from reverse to drive. I just have to get around to changing them. I'm kinda used to the idle shaking though, I drove an Escort for 5 years before the civic, and anyone who's driven an escort knows they all shake on idle... some idle vibration is normal for a front drive four cylinder.

If it was doing it while driving to I would say possibly an inner cv joint, too since that wasn't mentioned already. the inner joints wont usually click like the outer joints will, but they will vibrate really bad if the grease comes out and one breaks.

And by the way the motor mounts shouldn't be more than like $40 a piece... you do not need racing mounts unless your going forced induction with big HP numbers. The sacrifice of comfort is not worth it on the street, my friends 96 eclipse GST sucks with solid mounts in it, great on the strip, but hurts on the street.

 

+1