My mercedes c280 4matic started not shifting but would correct itself if I stopped and took the key out. Befor I could fix that the fuel pump went. I replaced the fuel pump and it runs but isnt shifting out of second at all now. Except it's not in limp mode because its revving super high. I checked the maf sensor and it's ok but I noticed on the side of that sensor is an empty pipe where a hose is missing. I capped it and my car started idling way better. It's not supposed to b capped tho i dont think. What is that thing and where does it go??