Originally Posted by Alastair (Post 3163815)

X2....

Worth checking the Air and Fuel-Filters are good, and any/all turbo hoses are tight and not leaking...

You could stick some 'Millers' or similar fuel-conditioner/injector-cleaner in first then-

Drive it like yer stole it, to blow the crud outta the exhaust system, running up to max revs for a short time at full throttle--while driving.
--Prob notice clouds of greyish/black crud in your mirror for a bit which should/will clear, at sustained full power.

Then re-test.

Used to be a Tester here in UK--and this was the general 'cure' for this problem