Egr codes appearing. Possibly a vacuum issue?

I have an allroad c5 2004 2.5tdi. I have had a couple of issues where my Mil comes on and the code indicates an egr insufficient flow error. I have cleaned the egr valve. Not that it was dirty really, and used a vacuum generator to test the diaphragm. All seems OK. The light reappeared on the way home today so that hasn't cured it. I had wondered whether the vacuum pumps deteriorate on these engines. Should I be checking it. If so what pressures make for a good or bad pump. This also had me wondering if the check valves in the vacuum connection to the servo ever fail. I need to replace mine anyway as I broke off one of the nipples where the small hose attached. I have looked at elsawin but I can't see a procedure for testing any of the vacuum system.

Any body else had similar issues?

Thanks Mike

If there is a problem with the vacuum pump then the brake pedal will be very hard to stop and the turbo cannot provide the necessary pressure either.
Check out the N18 (the EGR Operator) and Vacuum Tubes

I would suspect the solenoid if there are no vacuum leaks.