i have a 1986 300e. i am a teenager going into mechanics and this is still my first car. it has about 200,000 miles on it and it has ran fine until now. it had a major vaccum leak a while back making the same symptoms. i fixed it and about 6000 miles later it is worse. it vibrates at all levels of the rev range now. it feels like a motorcycle engine right now. this just stumps me because i checked ignition and vaccum. all seems to be fine. my possible solutions are: loose valvetrain(ie. cylinder head retaining bolts), bad bearing somewhere near crank throwing off balance, bad compression in one of the cylinders, or just bad timing. has anybody ever had a problem like this on their e-class? i need help in troubleshooting this.