Thanks for the suggestions. The new MaF was a genuine bosch, and made the car run exactly the same as before. (at least i have a spare!
). I haven’t checked the turbo internally yet, but the test I’ve just done would tend to point to it as the problem.
I've just done a logging run, Actual boost pressure vs desired boost pressure. If I keep it above around 3000k actual and desired are both pretty much spot on, with a slight delay between the 2 as you would expect. if i put it under load low down, Actual pressure never seems to get anywhere near desired pressure.
so to test the VNT i tried what 'got one two' suggested above. unplugged the vacuum pipe and went for a spin, found very little power below 3k. then i bypassed the boost control valve and went for another spin. back to mediocre power bottom and, nothing at the top. so the veins are defiantly moving to some extent. so what i'm now thinking is, rather than the veins being stuck, is the actuator calibrated properly? perhaps when the adjuster arm should be pulled out to its maximum at idle its only 3/4 out, and when up to speed the arm is hitting a stop before the actuator has fully extended.
i think this weekend I'll mark on the turbo housing the range of movement the actuator allows, the take the actuator off (without changing its calibration) and check the arms range of movement on its own.
i tried doing all of this along time ago, but the logging results where alot more random then. Possibly to do with the clogged intake and bad timing that Smaky (who spent most of Friday (in-between every obstacle the day threw at us!) and all Sunday night) put right.