GREAT JOB....
Carbon deposits cause EGR valve to stick
Stuck open The engine will idle rough and possibly have repeated problems yet run good at part throttle and under load.
Stuck closed may not have any drivability complaints other than check engine light on. Maybe some pinging at part throttle.
Most common cause of EGR flow trouble codes is a plugged up intake passage. Deposits form in intake passage when HOT exhaust gases rapidly cool when entering the low pressure intake manifold.