Originally Posted by gmercoleza

Do this: Put the car in neutral or park and note if the "rough" idle or chassis vibration is there. I'm guessing it's not. Now, put the car in D with your foot on the brake. Is the vibration very evident now? I'm guessing it is. If so, change the mount on the passenger side. It has collapsed due to the direction of torque and because it is near the hot exhaust manifold. Just get one off Fastlane or eBay and swap it out. You'll be shocked.

As for the hunting idle, just clean the throttle position sensor. I think Duke gave me the suggestion about a year ago when I experienced the same thing. Spray some carb cleaner on it, then some WD40 and it will go away like magic.

These problems are common on the 300E. A few bucks for a motor mount or two (depending which side of the debate you're on) along with a few shots of carb cleaner and WD40 can practically give you a new car.