My 95 avenger has about 120k miles on it, and for a while now it has been vibrating at idle. My idle RPM is normal , around the 650-750rpm range. Ive changed sparkplugs, air filter, fuel filter, EGR valve, PCV valve, Engine Mount, IAC motor,Ignition Coil block and wires, Injector and combustion chamber cleaning, but the vibration still continues.
 My oil pressure has also been way below normal at idle, but when I go above a certain speed it goes up. The oil pump is still good and Ive changed the oil recently.  What else could be wrong with this frustrating problem??

 Thanks in advance

The mounts and supports are good.

In the display panel I dont have any 'check engine' lights so that kind of rules out any sensors, Ive also been told that it could be a vacuum leak or the harmonic balancer. 1st of all how would I go about checking for vacuum leaks??  Any more suggestions are helpful.

Thanks