To help clear things up, call the 1-888 number in the partsShop. We have Phill on the phone to help.
If you are standing in front of the car with the hood up, the duo-valve is located to the right side of the engine under the plastic cover...above and behind the light assy. It has rubber hoses hooked to it and two wires. Also it is made of plastic and has two metal round things on top.
We are not saying 100% that it is the cause, but it is where to start.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS