I bought a 2005 Honda Civic Vti Prosmatic few months back.
When I first turn the car on and the engine is cold, I can have the car stopped (in gear) and it will not shake. The idle RPMs will be at 750.
After the car has heated up, I notice the idle RPM drop by about 250, and the steering wheel/car begin to rumble and shake. If I keep my foot on the brake and then tap the gas just enough to raise the RPMs back to 750, the shaking stops.
In neutral or park (it's an automatic vehicle) the shaking diminishes but the RPMs also rise to 750.