Need EGR help guys. Ford 3.8.

[williambishop]

Okay, check engine light comes on, error p0402(excess gas return). I replace egr valve(old one was pretty corroded and carboned), and it runs great for about 10 miles, then suddenly it's surging slightly again, and the check engine light is back on. Try again, same thing. While the ECM is learning the engine again(about 10 miles or two on/off cycles) it runs fine, but then when the engine computer is programmed, it runs rough again. I understand it could be anything in the egr system, even build up in the egr channels in the upper intake. The car is a 95-96 windstar. Anyone got any suggestions, walkthroughs, ideas...anything? Did a spark plug, all fluids, filters, etc...about 3 months ago. Someone said next thing to check would be the DPFE, but I don't want to repair this by purchasing parts until I find the right one(I disagree with that system of repair both on principal, and more importantly on budget). What I need is someone familiar with this who can step me through. I have the ford repair CD's for the model, and the haynes, so I can do whatever procedures are recommended. Anyway, help........anyone?