I've had vibration at idle, in-drive, ac-on and brakes pressed. I did everything, change plugs, cleaned MAF, ICV, etc... Lately when my oil was low (i have oil leak), I heard a rattle coming from the front of the car. So I suspected the vanos seals. I bought a rebuild vanos off ebay. Last night I swapped it out and the idle is smooth. when AC is on I can see the rpm rises to 980. No more vibration.
My vanos was original with 172K miles. So it was not performing for years now.