what would make my car misfire intermitenly while driving and also when ideling on 2005 Chrysler 300

has had new spark plugs and wires and a egr valve replaced

2 answers
Was the misfire diagnosed before the parts changed ? If so , what cyl(s) had misfire codes? Why was the EGR valve replaced?
seek a diag and have codes read and do not drive this could cause eng damage