Hi guys I have a 1999 Mercury Mountaineer with a P0401 code it says insufficient egr flow when i hook up my tool. I read on a lot of forums that most of the time its the DPFE sensor on the back of the engine near the fire wall. I bought the one at autozone and replaced it with no luck. The original one in the truck wasnt aluminium so im assuming someone replaced it. I didnt clean the EGR valve but i put my vacum gauge up to it and drew a vacum and the valve closed for sure because it started spitting and sputtering like a harley. All the lines look ok and i cant feel any leaks off the egr line from the manifold. What should my next step be? tight on money dont want to keep throwing parts at it is there a way to test the selonoid?