Do a search on cleaning egr line. You use an old piece of speedometer cable and "roto-rooter" the line out from the egr valve to the intake manifold. I do not get too concerned with the stuff that gets rooted out going into the intake.
Make sure that the piece of speedo cable bends easily at the very end to insure it gets around any sharp bends in the line. I have had to do it on my E320. It will make the check engine light come on and give you a "faulty" egr code if it gets completely plugged.

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Jim