starts when cold and stalls, won't start, runs great when warm?

My TDI passat runs great when it's warm. In the cold, it starts right up and then stalls and won't start. Have tested the glow plugs, they're good and installed new fuel pump. Anyone know what this might be?

Also replaced fuel and temp sensors

Won't start as in what? Does the starter turn over? Engine not catching? Is the tach registering rpms when you are starting or does it stay at zero?

When it starts then dies when it is cold, does it take for ever to restart?

try ing a few things like ,,,seperate fuel supply with primer bulb and prime pump see if that changes anythng ,,,,look for air leaks ,,

Don't want to hijack a thread, but I have sort of the same thing going on. 2005 B5.5 wagon. timing is on, torsion is good, no codes (I have VCDS) but below -12C it starts, runs very briefly (1 sec), then sounds like the timing is advancing, and it stalls with a very distinct change in tone (more rattle). You can crank and crank, it will maybe restart and do the same thing, but more often, it will chug along like it was really cold and juuuuust trying to start. when or if it does fire, it marks it's spot with a soot bomb out the tailpipe. During all this, there is plenty of fuel, tank pump has pressure at filter... Engine is 320000km, stock, fresh-ish stock cam, changed when I de-balance shafted it a year ago. Runs great with more or less correct mileage when it's warm. I'm kinda stumped too. Would a cam position sensor on the way out intermittently do this? and leave no code. It's pretty frustrating for an otherwise really reliable car. Thanks in advance for your help...