Diesel Engine EGR valve assembly separated into two parts. Black body part is motor with position copy sensor and white metal part is valve. In my opinion. Rotation part is easily blocked by carbon which is slowly build up leaking through valve.
If the fault code show EGR valve stuck or block then possible that carbon build up internally and blocking EGR valve openings or closing.
One of worst case I have seen, car was towed in cause it hard to start engine and even if succeed to start, it has no power to drive and no acceleration.
This car has EGR permanent fault code and it was stuck open the EGR valve and exhaust gas directly goes into the intake manifold and cause malfunction of engine.
