seat tdi vnt 110, sudden loss of power accelerating lots of grey smoke

went accelerate from a low speed in first or second, and all of a sudden the engine seemed to stop firing on one or more cylinders and there was loads of grey/white smoke from the exhaust. its seemed the more i tried to accelerate the worse it got. so in the end i turned off the ignition, no change, so i dropped into first, i think, and tried to rev the engine hard and all of a sudden the power was back and the smoke cleared. what could it be? the only other issue which i have is a strange noise when i come off the gas sometimes, which i think is the clutch flywheel springs. i hooked up vagcom but theres no error codes, appart from the usual pressure code because my vnt is sticking.

update

heres what its still doing:

if reved high when cold it either cuts out and wont start for some time, and sounds like theres no compression. or, also after the wont start problem, itll just run on a few cylinders and beltch smoke until, after some gentle reving, it seems to un stick something which then alows the engine to rev, and the smoke clears. the last time it did this i was accelerating and when i finally got it to clear it made a loud rattling noise for maybe a couple of seconds. almost as if the valves were stuck open.

the valve trian sounds tapetty as if the hydraulic liffters arent getting enough oil. but again some days it sounds ok.

theres a strange sound when i come off or on the gas. its almost like a chattering sound, like squirrells, that slows and stops, and doesnt come back until i repeat going on the gas then off. the motor engineer at work said it was the turbo. though i havent noticed any loss in power or oil burning.

the eternal vnt problem. which if i go for a hard run goes away for a while. only to return when i least expect it, usually while trying to overtake.

had my vag-com on it and only one code seems persistant, which is the overboost due to sticking vnt.

i have extended the glow time in the ECU, as it would start from cold then stop imediately, i would then start it and have some smoke for a few seconds. yes ive tried replacing the glow plugs.

i have done the soft EGR mod also.

p.s. the vag-com says the engine temp is 81-82c even after a run, but the dash gauge says 91c. also the gearbox is hard work/snatchy when cold. ive tried changing the oil, with no real improvement.

appart from the above the car runs fine and returns good fuel economy.

well

i think the turbo's ok, as once the engine sorts itself out the car drives fine. its almost like the valves all get stuck open, and then gradually reset.