Okay so I have seen this in several other forums about this happening and everyone saying a multitude of different things. I have a bmw e46 325ci 2003. I don***8217;t know what it is I have scanned for any trouble codes and have not found anything. Basically I***8217;m driving at a normal speed (around 40mph) then the car will have an rpm drop and have a vibration attached to it. I know it***8217;s not transmission because if it where transmission the rpms would surge and go up. I have replaced the fuel pressure regulator/ fuel filter and I have put in bed spark plugs (NGK laser platinum). If anyone can help me thank you it would be greatly appreciated. Also I do suspect it is vanos and I have a rebuild kit ready to rebuild it Incase it is the vanos. The person I bought the car from had a bunch of new parts valve cover gasket oil filter housing gasket and an oil pan gasket. Thanks for reading let me know your thoughts!