There is a few things to check starting with vaccum sol. follow the vaccum hose which i think its green back it should join up with a red line at that sol. the valve should look like there is a top hat on it be careful and pull it off there should be a filter in it lightly blow the filter clean and the valve.
2. the other thing too check is at the exhaust line to the egr there should be two small hoses that go to a sensor called d.p.f.e. make sure they are clean. and if everythinf is okay i would believe its the d.p.f.e sensor the basic number is 9j460. | 
