P401 Error Code - 1.9TDI EGR Valve diagnosis, cleaning. Plus Black box valve manifold noise

[DXX]

Hi All,

I hope someone out there may have the answers to my questions

Car: Seat Altea 1.9TDI (55 Plate)
EGR Valve: Diaphragm type (part No: 038131501AF)

The problems started when the 'Emissions Workshop' warning and engine light came on a few weeks ago.
After buying a code reader I diagnosed a P401 fault code that related to 'EGR insufficient flow'

I saw that you could test an EGR valve at engine idle by applying a vacuum to the diaphragm and the revs would drop/come close to stalling. I rigged up an air cylinder and tube to create this test and nothing happened which made me think that the EGR wasn't working, but then was my vacuum too weak? Or did I not know enough about the type of EGR valve it was?

Then following searching on forums I decided it was worth taking the EGR valve off and having a look. There was grime/small bit of oily residue within and around the pintle shaft, carbon build up on the bottom of the pintle where the exhaust inlet connects and some oil looked to have been leaking from a vent hole beneath the diaphragm and out onto the rear of the engine.

I cleaned it up with carb cleaner and scrubbed it accordingly. re-assembled and cleared the fault.

I half expected the fault to return and it did.

Then I also identified another issue that could be the problem and not the EGR valve at all. There is a block box valve manifold which feeds the vacuum to the EGR valve and when the engine is turned off this box vibrates and makes a wheezing noise for 3-5 seconds. it is obviously an issue and my wife who drives the car said that the noise has been about before the fault appeared, so that could be it!

Finally I did some more research on EGR valves and discovered that there are positive back pressure EGR valves that require at least 2000rpm before the valve can be opened by the vacuum. this is achieved by exhaust gases travelling up the pintle shaft to push on a second diaphragm. So I'm thinking that my test was incorrect and that I didn't clean the valve properly because I didn't look at clearing the inside of the pintle! and I want to eliminate the EGR valve as the problem part. So now I'm thinking restrip and clean the EGR in particularly the inside of the shaft.

So to recap on what would be helpful if anyone knows the answers

1. Is this VW EGR Valve a 'positive back pressure' type?, i can't find out on google! i.e. is there a hole in the pintle shaft that you need to make sure is clean through? (picture of the bottom of the EGR below which I thought I cleaned.
2. How can I be sure that I have applied enough vacuum to the EGR valve to test it manually and discount it? can I temporarily route another vacuum pipe from the engine? If so which one would you choose?
3. Is the noisy valve manifold containing the solenoid for the EGR valve the likely issue?

EGR.jpg

Thanks, James