Idle "surges" and the associated symptoms are actually quite common with these engines. But a variety of issues can cause them, making troubleshooting difficult.

I too, have the annoying idle "surge" and have solved just about every other problem in that car over several years...EXCEPT the surge!!!

The most prevalent cause is a vacuum leak. Check all vacuum hoses for integrity or any that are loose...they should all fix snugly enough to not be able to pull them off the connections without some muscle.

The MAS (or mass air sensor) is another culprit.

I've also read about the neutral/backup safety switch and the intake manifold leak as possible causes. However, I don't recommend "throwing parts" at this problem, as MB parts can get pricey, and it's frustrating to do so and still not fix the problem.

Do a search on "surge" or "surging" and you will find that many others here have struggled with this!

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car