As I found with my W124...the center vent pod was working, but not to its full potential. You may find yours is the same issue. Its working, but only partially opening.

Mine held vacuum only up to a certain point and no matter how much more I pumped with the mityvac it wouldn't go higher.

I got a good 30% more air volume out when I changed it.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k