Sticking EGR or plugged egr tube to intake/head.
Easy test is apply vac. at egr at idle.. If car runs rough with vac and smooths out when no vac. , the tube is clear and valve is working. [ make sure it SNAPS back when releasing vac.]
If all checks out , look for vac at the egr vac hose with a gauge.
[ You will have to gas it , as egr is not called for at idle.]
If no vac, check hoses to/from switchover valve in front of engine.
[under front cover.]
There was a EGR upgrade TSB, but check these first............