I thought it was an engine miss
 

For several months our 2003 E320 has been running rough as I called it.

Over the last few months, I changed the 12 plugs, put in fuel injector system cleaner and changed where I by fuel, but the missing as I called it, slowly got worse.

My wife finally watched an online video of a MB shaking while in gear. It was motor mounts failure.

Yesterday, I changed out the E320's engine mounts here at home and found the problem.

The drivers side mount was bad and had been leaking slightly.

What seemed like an engine miss to me turned out to be a bad motor mount.
Just to help someone else out I posted this.

I forgot to say..

The engine runs so smooth now when we stop at a light, it sounds like the engine stops. We got so used to a rough idle and it was the engine mounts all along.

Yup, common problem
 

I had the same thing happening on my 560SEL, replaced the motor mounts, and it smoothed out for a couple of years. Now it was running rough again, this time a vacuum leak on the plenum seals. I am replacing them right now (a massive job), and one of the seals separated in my hand, with the inner ring detaching from the outer ring. What a mess!