I thought I would let you all know about recent problems I had with my T4 2.5 tdi. I have average to good amateur mechanical skills. When warming up I had white smoke coming out of the exhaust until it reach normal running temp. but would still stink. I also had intermittent heavy steering during warm up and fuel economy was lousy. The engine was rebuilt approx 30k miles ago. After reading a few threads here I bit the bullet and put it in for a cam belt change and for them to check all the timing including fuel. They found that as well as the fuel pump being out the crank pulley was cream crackered moving by 4 to 5 degrees. So a new crank pulley fitted, cam belt, waterpump and all set up by computer , what a difference. No smoke, better fuel economy, better acceleration, better steering. So my advice is If you get these problems don't tie yourself up in knots every morning like I did looking at the smoke wondering where to start, get it sorted professionally unless you have a mate in the trade, there isn't enough info on the web to do this yourself and specialist equipment is needed, pricey but worth the good nights sleep and it shuts the neighbours up taking the p**s. I hope this helps.