1999 Mazda 626 Engine vibration at idle 650 RPM

Checked cyl compression after warm up. 2 adjacent cylinders read 30-60 psi, 6-8 revolutions to get to 60 psi. Pulled head, had valve job done, and replaced rings on all 4 cyls. Have about 100 miles on new rings. Runs great at every rpm except idle when warmed up. Steering wheel still shakes as does the hood especially when the a/c is on. Very aggravating and violent vibration. I had replaced the timing belt and other belts and 3 engine mounts and 1 trans mount[lower]. All mounts where ripped up really bad. I have already sunk $1200 or more into this abortion. Raise the idle to just above 800 rpm and the vibration is non-existent. Could there be a problem with the idle circuit in the computer? Bad o2 sensors, partially clogged catalytic converter? New platinum plugs where installed and the timing is right on the mark per manual. The ignition timing is, according to the Haynes manual, 11-13 degrees BTDC. With a timing light it reads from 10-12 degrees warmed up in park at idle. I'm looking at the o2 sensors next. What would be your guess? I hope the answer will not cost me $1200 or more. If it does I'll tell my son to just use it as-is. It vibrated in park or in neutral
Mike.