Thank you for using just answer. This can be caused by several things in the EGR system, most commonl;y carbon deposits, click the link below, the system needs to be tested:
One last note on your last response (thank you for the reply by the way), the EGR pipe on the back of the motor is nothing to worry about on this. This is NEVER an issue for your stated concern, they do tend to crack and produce exhaust noise with mileage/age but will not cause EGR codes, also you would have to remove the transmission to access this pipe.
Your issue is most likely related to carbon as you indicated your theory was. The download I posted shows how the system is laid out and how it interconnects. Most liekly the EGR feed port that runs to the throttle body has backed up with carbon so once you get the EGR valve off be sure to clean out the port with intake cleaner/pipe cleaners/compressed air and most likely you will need a new modulator valve as well.
Good luck and thank you for using just answer, you are a valued customer to us and your positive feedback is always appreciated!