I have quite a few different EGR Valves.

I have removed the Heads, where the Vacuum Hose attaches to the Diaphragm, from each EGR Valve.

I have noticed that Air Leaks between the Shaft and Centering Collar on each one. Some Pierburg reference, I believe I read (in German) a certain specification for leakage.

Unfortunately, when the EGR Valve is reassembled, the Air (Vacuum) drawn from the Inlet Manifold to the Cast Iron Body of the EGR Valve leaks sufficiently to cause a rough idle. I sprayed some aerosol lube, at the shaft and collar, when the car was at idle. The RPM increased and smoothed.

I have read from someone else who posted a few weeks ago that his car was the same.

Does anyone know if, in fact, the air leakage is normal, even with a new EGR Valve? The only way I can see that it would be prevented is if the Shaft was tapered ( >|) as it slides toward the Collar. As far as I can tell, using my calibrated eyeballs, none of the shafts are tapered and any friction from a tightly sealed collar around the shaft would impede the motion of the shaft. And, that is precisely why the EGR Valves fail.

The carbons and oils and whatever coats the shaft to the point it does not slide in and out of the collar. That would be a significant design flaw, as a tapered shaft would prevent that. A side benefit . . . no vacuum leak and a smooth idle.

Any thoughts and information would be appreciated.

However, do not reply with removal of the EGR system or blocking it off. It was installed for a reason: Reduction of NOx, while as a side benefit it reduces the Combustion Chamber Temperatures, which reduces the conditions for Pinging.