What would cause a 1999 VW not to start on cold mornings but run perfectly any other time?

I have a 99 VW Passat. Having it not start has happened to me, several times, and it is infuriating. Esp. because it seems to be related to the computer. Did you happen to have run it for a short time, say, to move it in the driveway or something, and then turn it off? And then, the next time you went to start it, it wouldn't start? A mechanic told me that something in the computer gets confused if you do that--to never just run it for a minute and then turn it off--let it run for at least 5 mintues. I've had to have this car towed more than any other car I've ever owned, and I've owned an old Alfa Romeo and a Ford pickup. Grrr. Good luck.

It's the coolant temperature sensor

Engines need a richer air/fuel mixture when they're cold than they do when warmed up. They can do this in several ways--dump in more gas, cut down the amount of air or screw with the ignition timing.

There are two problems described here, and both are caused by the same thing. The first is that the car won't start in the cold...which means the sensor is reporting the car's warmed up when it's dead cold. The extra gas the engine needs isn't coming in, so the engine will not start. The other, where the "computer is getting confused" after you start, shut down after a minute then try to restart, is that the engine isn't warmed up yet but the defective sensor claims it is. The engine still needs the gas, but it's not getting it so you don't start.