if you cleaned the tube and the valve is good I think the experts here would agree it must be the ports in the cylinder head that are blocked. Small passages at each exhaust valve which carbon up. I rebuilt my head in this car and the machinist did a great job cleaning these ports. Im not sure if seafoam cleaner or other solvent processes can do it..

And Im not sure if I agree that blocked egr passages will cause a rough idle..

I will be curious to see the comments on this.