[mbtoloczko]

Having a meter hooked up the one of my stock O2 sensors has been very informative about how the motor functions. I've found that the vibrations at idle in my car vary with the a/f ratio fluctuations that are a normal part of ecu operation. At idle (and up to about 20-25% throttle), the ecu is in closed-loop mode and is constantly adjusting the a/f mixture. The result is that the a/f ratio swings back and forth between lean and stoich at a fairly regular interval of about 2 sec at idle. I can feel the intensity of the motor vibration vary with the cycling of the a/f ratio. If the vibrations are really strong on your car, it may be that the O2 sensors need replacement. That's just a guess though. The O2 sensors on my car are in good condition, so I don't know what bad O2 sensors do for the cycling of the a/f ratio. It could also easily be something that svx_commuter mentioned that is causing the a/f ratio to swing to leaner or richer ratios during its cycling.