Truck is a 97' scab, 5.4, auto, 4x4. Check engine light is on again and showing code P0401, egr insufficient flow. Have already replaced the dpfe (spelling) sensor. Need to know what to try next.

 

Are all your vacuum lines good? I've got a 97 mountaineer that had the same code, and the vacuum line on the egr valve had dry rotted. It looked fine but disintegrated when I tried to pull it off. I also threw a vacuum pump on the egr valve to make sure it would open, and it did.