Confidon42

Hey guys I have a 2004 E320 and recently pulled off the intake manifold and put on new gaskets. When I put everything back together, I had this plug sitting right underneath the yellow connector under the egr pipe. I was at Mercedes grabbing a gasket and the part guy came out there and had no idea either. Hes actually helped me a bunch, so he wasn't just trying to get me to take it to service. Ever since then the cars been having a lack of power in first gear. Also when coming to a stop, it idles high sometimes and has even lunged forward like it was given gas. If anyone could please help me, I'm a little concerned and wanted to have an idea before I take everything off again. I took a far away pic and close up so you can see where it's coming from. Hope to hear from someone, thank you.