I took my ML320 to a local parts store because it was idiling poorly. They checked the codes and a PO400 (egr flow) came up. I tried cleaning the tube that goes to the egr valve last night. The tube was not blocked and that didn't help. I also cleaned the maf sensor and put seafoam in the gas and that did not help either. What all is involved in replacing the egr valve? Does anyone have any other suggestions of things to try? Thanks!