Electro valves...

[wheeler]

With engine off apply vacuum directly onto the EGR valve & it should hold vacuum. press the release valve & you should hear the valve snap shut.
Next test you can do with Mityvac connected directly to EGR valve. Have engine idling & live data readings up on diag tool. Check to see if the airflow reading drops as you open the EGR valve.
Remember when disconnecting any vacuum pipes off the components when the engine is running to temporarily plug the pipe with a small bolt or screw so you dont have a vacuum leak.

[Rhothgar]

With engine off apply vacuum directly onto the EGR valve & it should hold vacuum. press the release valve & you should hear the valve snap shut.

Obvious really. Sometimes easier to ask someone with prior knowledge than struggling to re-invent the diagnostic thought process wheel...

Next test you can do with Mityvac connected directly to EGR valve. Have engine idling & live data readings up on diag tool. Check to see if the airflow reading drops as you open the EGR valve.

Not so obvious so thanks for that.

Are those screenshots from the Mechanic's Handbook? I never think to look there.

There is a separate tool not shown there for connecting a vacuum gauge between the butterfly housing and a intercooler pipe.

[wheeler]

Only ever used a Mityvac that has the pressure gauge built in. It comes with a verity of T-pieces etc for different applications.

[Rhothgar]

Only ever used a Mityvac that has the pressure gauge built in. It comes with a verity of T-pieces etc for different applications.

Not sure whether to update on this post or my other post but I got the HDi running well yesterday (Sunday) and it's not pulling like a train again.

I will type up a full report later today if I can make the time as I also have more questions relating to vacuum pressures in particular at the vacuum pump itself as the manual I have (which I believe it for the 90bhp? (DW10TD) for RPO 8211 on states that it should be 1 bar (30" Hg) vacuum at idle. I measured 22" Hg at the end of the pipe that pushes onto the EGR inlet (or was it on the outlet? Tired now!).

I have some observations to report along with detailed questions. A bit more hypothesizing basically but it would be really useful to bounce it off someone who really knows their stuff.

Next stop is to try and get the fuel consumption back on track so I think I am going along the lines of:-

1) Test vacuum at pump and fingers crossed it's 1 bar else consider changing AFTER (EDIT: Just referenced the 2001 S2 Mechanics Handbook which has RHZ in it and that states 0.8 bar at pump),
2) Renewing all vacuum pipes anyway and using crimpable clips to ensure airtight connection (I'll explain why later!)
3) EGR clearly maintains vacuum in a fashion (there is an extremely slow leak but cannot rule out diaphragm as I did not test straight off the EGR valve connection itself).
4) Replace MAP sensor as turbo pressure setting is some 140 mbar above the reference value of 1013 mbar. This may then resolve the high MAF readings I am guessing as the high reading is perhaps causing a slight overboost and therefore overfuelling.
5) Consider replacing MAF sensor with a high quality Siemens one if no improvement if above cheaper work does not result in lower MAF readings.
6) Replace injectors if all the above does not result in a 50 mpg return on a good run.

Does that sound like a reasonable methodology to you, Wheeler?