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The manifold is not leaking. The codes, P2004, is related to the tumble flap in the manifold. Now, there are a few things that can be bad. The actuator, a wiring issue, the flap itself, loss of vacuum to the switch over valve, damaged linkage, and the list goes on. And yes, it is most likely the cause of the P0301.
To start, you need to locate the vacuum supply to the switch over valve. The supply is in the front of the intake manifold. Take a look at picture one. Locate the #2 vacuum hoses and check for damage. Picture 2, the arrow points at the vacuum supply. I have to be honest, the hard plastic tube which the rubber vacuum hose connects to commonly breaks. If the vacuum is good, my next guess is the throttle actuator on the front of the engine has failed. Commonly, the plastic linkage which actuates the tumble flap (via vacuum to the switch over valve) breaks. If you look down from the top of the motor (center) you will see the plastic linkage. Make sure one of them is not broken. If one breaks, it will set the P2004 because the sensor will not see movement of the tumble flap.
Now for the crazy news. If that is the problem, Mercedes does not sell the plastic linkage separately. They expect you to purchase the entire manifold. However, if you check online, there are companies that are now manufacturing repair kits.
Check these things first and let me know what you find.
Images (Click to enlarge)
Tuesday, November 13th, 2018 AT 7:19 PM