could somebody give me some advice my 06 a3 2.0 tdi seem to give out white smoke some of the time takes ages to get up to temperature.when driving it seems to go a bit then lags then goes again.havent noticed it losing water.read on internet it could be egr cooler or egr valve or oil cooler anti judder valve or even the head gasket any help would be appreciated so I can narrow it down a bit thanks.