since the idle of the car has become rough i would agree with the egr valve needing replacement
to test you need to apply a vacuum to the valve, it idle gets worse then the valve is fine, if no change then the valve is bad
if it tests fine then i would check the DPFE sensor but this doesn't sound like the case
I am not sure how hard the egr valve is to change, if I am thinking of the right thing it is right on the top right corner of the intake manifold
