I know mine shakes badly at idle.. but with the cam its like idling with a dead miss on 3 cylinders, and I'm using poly motor and trans mounts
.. but hit the gas at all and it smooths right out..
Some ideas : motor mount, trans mount.. If its a manual.. your car could have puked a flywheel weight, if its automatic it could be the torque converter
Check your balancer, make sure there's no mud or crap caked in the pulley.. or any of your pulleys at that... remove the belt, and with your hand check to make sure all the pulleys are tight and spin as they should (IE power steering pump should have some resistance but should not make noise and should have close to no in/out motion..)
Also try unplugging the wires one at a time (expect to get zapped now and again, would help to use spark plug wire pliers..) if the way the motor runs changes with each wire you pull, then its likely not (at least not a dead cylinder) a misfire..
It could still be a lean condition (lack of fuel?) causing it but revving it up a little would usually clear this up (esp as it revved back down to idle)
if your flywheel is warped too badly (from heat/damage.) that could also affect it, if its a flex plate (auto trans..) it could be cracked..
that's where I'd start...