engine vibration at idle

[jimtash]

I have an '89 SHO with a vibration at idle only. It actually feels like something rotating around from the drivers seat. The engine does rock slightly back and forth but as soon as I step on the gas, it stops. I checked the codes and replaced the plugs and wires and still the same thing happens. This is a rebuilt motor with 30,000 miles and I did use Shonuts motor mounts when it was put in and wonder if that's the cause of it but I don't know. Someone even said it the engine could be out of balance but wouldn't the vibrations get worse as the rpms go up and not disappear? Anybody know what could be up?

 

[SHOman247]

could be flywheel related...do you have a light weight one? causes vibrations at low rpm's due to the low amount of recipricating weight but has the rpms rise the rotating force balances it out.

 

[jimtash]

No lightweight flywheel.