1986 Honda Prelude Idling Problems

Hello,
I have a 1986 Honda Prelude Si. The dash and front end of the car vibrates loudly and terribly when the car is idling. Also, it doesn't idle evenly; the needle fluctuates. If I gently press down on the accelerator, the idling becomes smooth and even and there's no vibration. I've had the following replaced: spark plugs, plug wires, distributor cap, rotor button, pcv valve and grommet, and front motor mount. I've taken the car to four different mechanics. They checked the following: all fuses, for any vacuum leaks (no leaks), idle boost solenoid, cold start injector, and all sensors. I was told that all idle parts were working as they should, and there's no air in the cooling system. I was told that the motor mounts looked a little weak, but they're not broken. One mechanic tightened the accelerator cable and adjusted the throttle in an attempt to fix the problem. At this point, everyone is at a loss as to what could be the problem. I would greatly appreciate any help you can give me. This idling problem is extremely annoying.
Regards,
Tyrell