Is there a ground bus under my driver seat on my 90' buick lesabre limited? thanks guys!

Also, what would cause, when cold, idle to go from 750-600-750...once warm it'* fine at 500rpm idle no ups or downs. Just when cold. any symptoms for that?

Also sometimes I have a mis-fire. If I wack the highest up coil with my hand, it runs fine, IS this a bad coil or bad connections or both? or could my ICM cause this? didn't start happening till winter.

Yes, there is a ground bus by the drivers seat under the carpet by the door. Check the techinfo as I believe there is a good article on how to clean it.

The idle fluctuation when cold is normal. It should go to a normal idle as soon as the motor warms up to operating temperatures, which shouldn't take long.

It does sound like a coil is going south, especially if it changes when you tap it. You could check the connections if you want, pull the coil and ICM assembly off and use a wire brush to clean all the contacts.