The DPFE sensor basicaly reads the difference in pressure between to given points in the egr pipe, one before and one after an orifice of specific size. The common problem is that the dpfe goes bad and gives the computer a low flow voltage reading so at low rpms it is actualy causing the computer to think it is not flowing enough when it is actually flowing to much, giving you a lean condition and an increase is sulfur emisions, hence the rotten egg smell. As is your case I would leand more towards the DPFE sensor than clogged passages since you are having running and emisions related issues due to the egr flow. If it were plugged you would not have those two symptoms.
