Idle, engine shake, rough?

Hi again people, Well when I start my car for the first time each day the car idle rough before it gets down to the normal operational rpm, which I think is fine, for my car is just below the 1, but it seems that the engine is shaking at normal operational idle, in a 3-5 second interval the engine shakes. I notice this before and I change my spark pulgs. but it stills shake. The car does not Hesitate at all, In the freeways it's fine I go up to 80-90 mph and the car runs fine, no engine light. Is there something that I'm missing? Do I need to replace something? is it the timing?
Thanks for your time again

Check the motor mounts. The rubber will crack on them and allow the engine to shake/vibrate.
The timing is possible, when was your last timing belt changed?