1997 Geo Metro EGR flow fault code

1997 Geo Metro 1.3 mileage: 117,000. I keep getting an EGR flow fault (P0400). I have replace the EGR valve, solenoid, modulator, and taken off the intake to clean out the EGR port. However I am still getting the same fault. I have plugged off the EGR valve vacuum and still flow fault. I don't know what else to try. I have run a vacuum check on all components, and all show to be working and holding vacuum. I don't know what else to try. I also had it in the Chevrolet dealership. All they did was clear the fault! And, said they couldn’t find anything wrong.