hi my 99 a6 tdi avant is having problems its really hard to start when cold and lots of blue smoke is coming out of exhaust also the car seems to die and cant get over 60mph i changed the glow plugs and put a new maf but has not cured it.thanks

 

I'd suggest you get to some TDI forum, as there are no diesels around here.

 

Blue smoke would indicate that you are burning oil, while white smoke is caused by water (either a blown head gasket if heavy or just condensation if only during startup), and dark smoke is fuel related (running rich).
If your problem persists after replacing the plugs I would suggest checking for compression leaks.