Thanks amacman.
This is what I found in bimmerforums:
Vanos Solenoid done... WOW, what a difference - Page 8 - Bimmerforums - The Ultimate BMW Forum
All this being said, most ppl i read on here run heavier weight oil. However being that I have no problems running what I run I dont want to change just for the hell of it.
(other than that occasional bump in idle, i have a 95 m3, and it only occurs if i put it into nuetral and coast to a stop... i am reading NGK spark plugs for 96+ m3 will help with this?? my bad off topic)
Many people do not realize this but vanos is COMPLETELY run on oil pressure alone. If you do not have the proper oil pressure you have no vanos. Imagine the vanos system as a dual oil path way maze. one oil pathway is for when vanos is not engauged, the 2nd is when the vanos is supposed to be engauged. the thing that shifts between the oil passages IS the vanos solenoid, thatts why it is such an essential part of vanos. without it you have no vanos. if the solenoid does not operate 100% vanos will not work properly. Lets say the vanos only has enough force to push change the machanism that changes the oil pathway 50%, well that means only 50% of oil will get into the "vanos on" pathway and thereby reducing pressure greatly which will then in turn only move change the cam timing by 6 degrees (instead of the full 12 as it is supposed to in the mid range).
Another factor that is essential is the oil ITSELF. it is the mechanism by which u push the vanos gears. If you use a really thin oil (aka mobile 1), it flows like water and it does not have the same oil pressure as a much heavier 15w-50 weight oil which is much thicker (think of molasis). the 15w-50 is able to "push" the vanos to the proper specs better b/c it has higher compression & oil pressure characteristics and is much thicker. so your oil is just a crucial aspect as the solenoid or vanos mechanism itself. Thats why you see so many people say "i replaced my vanos but the noise came back!" well duh! u are using the wrong oil or your solenoid is bad.
So basically... if you are have vanos problems here is the order you should replace things...
1) change to a much thicker oil (preferably a 5w40-20w-50, bmw recommends 20w-50 for a reason, but you can do castrol 5w-50 which will work in pretty much every weather condition & bmw recommend castrol anyways).
2) change vanos solenoid
3) then replace vanos unit if necessary (though I have spoken to NUMEROUS BMW master techs and every single one dispelled the "vanos stuck" myth. it simply cannot happen they say, jus thought i'd share that).
hope this info helps you guys out.