Purge Valve
This page is to explain my issues with the purge valve, this valve have to be put back to it's original location else it will create a loud knocking noise under your dashboard...intermittently....about 5mins cycle when idling. So next time..if you ever hear some noise ...check this , make sure it's at it's holder. more details at the link below. http://www.pelicanparts.com/techarticles/Mercedes-W204/61-ENGINE-Purge_Valve_Replacement/61-ENGINE-Purge_Valve_Replacement.htm