Update: Problem still there, not getting any better. Garage thinks it may be fuel pump on way out so are going to do a fuel pressure test.
Current symptoms are lack of power and black smoke on acceleration. Worse when engine cold. Slightly rougher running, especially on acceleration. Crusing is fine.
I'm not so sure though...I remembered an additional detail - the problem first occurred just after I suddenly took my foot off the accelerator whilst moving through water (only about 6 inches). I remember thinking there was a bit of a strange noise/clunk at the moment I did this, and I put it down to the water. I'm wondering if the sudden vacuum in the intake manifold could have broken my EGR valve (is it a butterfly or something at the manifold?), causing it to be constantly open. (I've been getting intermittent error codes about EGR stuck both open and closed)
Is there a way to test the EGR butterfly valve to see if it is stuck open? Or, is it a difficult job to remove it and visually inspect it?
(My turbo seems fine btw. Wastegate movement is fine, reaching full boost ~230kPa. Felt the pipes, feel firm - don't think there's any delamination)
Thanks!