Motor Mounts

I recently replaced 2 motor mounts in my '98 Corolla. After I replaced the upper passenger side one (under the washer fluid reservoir), I can now feel the engine vibrating a lot. This mount was a delear mount, but the lower one was. Any suggestions?

A new, stiff mount will transmit vibration to the car body.
Has basic tune up stuff been done so the engine idles and runs smoothly?
Have the valves been adjusted?

Might you have over- or under-tightened any of the mounting bolts/nuts?