Just came across this thread. White, acrid smoke is un-burnt fuel, its caused by leaking injectors or incorrect timing and its usually worse at higher revs, sometimes gets even worse when the engine is warm, thats when the un-burnt fuel gets to burn off inside the exhaust manifold.
My TD5 did it, have you had your injectors properly tested?
I sent my injectors for testing, its not expensive, around £30 each at a proper diesel place, like Merlin Diesels.
I did the unplug thing as well, it didnt help with tracing the fault.
One of my injectors was leaking badly, the others were fine.
Have you had any fault codes read?
Diesels have been around for long enough that this sort of issue should not be a long/expensive "treasure hunt"!
Mark