Thanks for the reply. I read that they should be between 8 and 10psi as stock. Just had a read of the sticky thread, it sounds basically like it could be a whole bunch of things, its a real shame the fault codes aren't more specific. I had a check of the hoses I could easily access yesterday after resetting the fault code and gave them all a little extra push on. Ill just have to see how it goes.

A smoke test sounds thorough, is it something most places can do?

Its not a 'specialist' job as such it just depends if they have the equipment, I would have thought some kind of pressure test could be done but a smoke test makes it easier as they'll see exactly where it's leaking.

I was just wondering if it had been tuned so a software issue could be ruled out, which is what my 17705 turned out to be. Pipework would be my first thing, won't always be easily visible, holes in intercoolers aren't unheard of but you wouldn't really see that for example.

pipework it is.

pipework it is.

I had exactly the same split, bit of a favourite place. Could explain it, however when I found my split I cheered as I though all was solved, and whilst idle and running got a bit better it didn't solve my boost drop off issue. Anyway it may solve yours, news fixing anyway so see what happens after. If it's still the same or only a little better try a smoke test.