Really appreciated guys
So, to explain fully & also help anyone who has this issue in future... I now think that it was the air doseur flap, the double "air doseur" as I understand it, (single on NON-FAP engines) is the plastic air intake thingy bolted with 3 x 10mm boots on its triangular footplate to the alloy intake manifold front of engine so nice and accessible, just before where the EGR pipe enters the intake.
This 'double' air flap has 2 separate flaps, each vac operated with its own vac actuator & elec control vac solenoid.
Now, (As i understand it) - 1 flap is always open EXCEPT in DPF regen mode, where it is closed by the ECU to bypass the turbo intercooler for max air heat during regeneration.
The other is closed unless running/accelerating whete it opens to whatever degree to allow correct amount of air in. THIS was the issue (I think, anyway!) Because when I jad it in my hand, removed, and applied vac to it, it was stuck closed, more and more vac was applied then suddenly it flew open with a loud click, then it was easy to open every time thereafter with the slightest of vac. Since this, the issue of jerking and hesitation / power loss has gone (around 1500-2000 RPM and usually on the warm up phase, but as it got worse, would sometimes do it at full temp but only very occasionally, 99% of the time once the temp hit 80° it was fine) Though it was always possible to accelerate past it / through it after 2000 rpm if I got fed up or needed to enter a roundabout without the hesitation! I hope tgis made sense.se and that I got this right!?
Of course, if the issue comes back, then I will report back on this thread. Thanks again! David.
