300 tdi smoke

I have a white or maybe slightly blue/white smoke problem with the engine hot and cold. Under no load if you hold the RPM at abut 2000 there is huge amounts of white smoke from the exhaust, if the RPM is decreased or increased the smoke disappears. The engine runs very lumpy when emitting the smoke
If you drive holding the RPM at 2000 RPM there is no smoke, lifting the foot off the accelerator there is a puff of white (ish) smoke. If you floor the accelerator in high gear when driving there is no smoke, the power output seems normal.

I have

1. swapped the injectors from my 300 TDI Disco no change
2. run with the engine normally aspirated no change but the engine runs very lumpy
3. run with the crankcase breather disconnected no change

does anyone have any ideas

tks

shunter

Check you are not loosing any water first - is the smoke thick or light and whispy?

It could be oil leaking past the valve stem seals down, oil from here can create white with a hint of blue smoke, due to the fact it is coming in the top and not getting a chance to burn well, whereas oil from the rings or flying in as a mist from a leaking turbo will burn very much blue/black.

How many miles is on the engine, 300tdi's about the 125K mark can do this.

there is no water or noticeable oil use, the smoke is very heavy and the engine has done just under 125K. Initially I was thinking valve guides/seals but I thought the smoke would have disappeared after running for a while?? I am also puzzled why it should only happen in a certain RPM range

tks