P1470 Fault

I have been living with limp home mode for a while >3000rpm on 2001 E320 CDI

Have found reliable source of getting fault codes and discover fairly common P1470 fault.

I am confident it is not the EGR (welded shut) and I have pressure tested the whole inlet with 20psi from compresor, removed swirls flaps cleaned manifold etc.

Reading all the posts I think it must be either the vacuum system or catalytic converter.

I have checked vacuum hoses and all seem to hold vacuum with my tongue blocking the end. Could I replace the solenoid with the now redundant egr one?

If this doesn't work I will concentrate on exhaust. How will I know if the cat is blocked? Is it an easy job to remove and inspect?

Thanks in advance