Jerky start and smoke, 2008 2.0L TDI PD BRE

[John11smith]

A six months ago I bought A6 SE Automatic 2008 BRE 82K miles, belt replacement sticker at 72K, air filter looks like new, perhaps filters and oil just fitted before collision, but have replaced oil and oil filter anyway. There is service book with nearly full history. Car was damaged category C, but there was only cosmetic damage quarter panel, brake light, bumper and key like scratches on another side. Took long time, but have fixed and repainted damaged parts myself. Car was not driven except outside garage to turn around and back, because I do not have trader plates yet. I noticed that occasionally it jerks on start. I thought it could be related with disconnected plugs in the boot, but after connecting everything back and clearing errors problem did not go away. It sounds much the same like after replacement PD injector. I fitted all injectors from another car, checked injectors and valve timing adjustments but still the same.
Over six months there was much build of condensate under oil cap and inside a top cover. I thought it could be normal because of lack of driving, but after cleaning and starting cold engine it reappears in few minutes. If open oil cap when engine temperature about 50C then much of white smoke coming from under it. At the same time heavy white smoke comes from exhausts. When warms up it settles, but there's still some.
Yesterday I drove to MOT. Never had to drive similar car before, but performance really not what I expected from 140HP car.
One of ceramic glow plugs looks like new. Possibly bit of an old plug fell inside cylinder and damaged it? Or belt was replaced wrongly and some valve is slightly bend? Any more ideas? How to check compression? Elsawin says to use guided diagnostics, but there is no such thing on VCDS.

[Imoptep]

My A3 2L TDi has the same ugly starting as yours except mine gets worse as it gets hotter.
A6 is a heavy car, i have a A6 Allroad 4f with the 3L TDi 179Kw and it goes well but feel a 2L would be quite under whelming power wise
engine is an interference engine no room for valves when piston comes up. Very surprised if belt was out a bit, maybe injection is out
White smoke in a diesel can be bad

White smoke: This is one of the most difficult symptoms to diagnose because a number of factors can point to two general causes: overcooling, whereby the cylinder head and combustion chambers operate at a temperature that's too low for proper combustion; and piston-ring blowby, which indicates low compression and poor combustion.
White smoke represents atomized fuel, very small droplets of fuel that form a fog of sorts. It's common, and quite normal, to see this when a cold engine is started and until it warms up. If, however, a preheat device such as glow plugs or an air-intake heater are malfunctioning, the production of white smoke may be excessive and longer lasting. In extreme cases, the engine may be difficult or impossible to start.
Fuel of poor quality, particularly fuel that's off spec or not properly formulated as Number 2 diesel, will burn poorly, which in turn may produce white smoke. Adding a fuel cetane booster may temporarily alleviate-and identify-this problem.
Other causes of white smoke are poorly adjusted valves or worn valve seats, a partially activated decompression lever, a blown head gasket, or a cracked cylinder head or cylinder liner. A mechanic with the proper tools can narrow down the suspects.

---

Engine Tip: White smoke can indicate overheating, but the "smoke" is actually steam that's produced in the exhaust system rather than as a result of an overheating engine. This may occur, for instance, because of restrictions in the injected elbow. To test for this, measure water temperature in the "wet" portion of the exhaust hose; it should be below 200F.