Just to let you all know that I have finally fixed my 2.1 SED XM that was suffering poor starting, idling and running.
It turned out to be the filter pump housing/primer pump. I had to get the car collected in the end and taken to a diesel specialist. Even they were stumped at first because the pump did everything it was supposed to yet air was still getting into the fuel lines. The housing was only a few years old and the car has a full history so I suppose it may have been a porous casting and/or cheap pattern part.
They fitted a genuine Bosch part that didn't cost the earth plus glow plugs, and the car now starts first time and accelerates like the Millenium Falcon!
I repaired the turbo boost air pipe with self amalgamating hose repair tape so it now revs over 3000 rpm with no ill effects. I will replace the pipe in the near future.
Once again a BIG THANKS to everyone who submitted suggestions and advice.
XM diesel problems solved!
Moderator: RichardW