1992 Holden Commodore Vibration through pedal

Hi guys. I have recently noticed with my VP Commodore (V6 Auto), a rough vibration in the engine whilst at idol. I can also veel the vibration through the brake pedal whilst at idol. However, when I release the brake pedal and accelerate the vibration disappears until I come to a stop again. The vibration exists regardless if I'm in drive or neutral. I have had all engine mounts checked and am told they are fine. Do you have any idea what may be causing the vibration. It just feels quite rough. Thanks, Leigh.