ur-q won't start cold

[RDG51@aol.com]

After thinking my car was well sorted for winter, and running just fine, last
night, after leaving work at about 1 am, I was suprised to find my usually
perfect starting car would not fire up...cranking only.  In the past I had
this problem, but had replaced everything, including what was ultimately the
problem, the air flow sensor, whose plate was getting stuck.  This time, I
was lucky, in that after a deft tap on the dome over the sensor with a metal
object, the car started. Of note is that the outside temp was around 10 F. I
have not used dry gas yet, but will today. The car started fine this am after
a night in the garage. Any ideas out there as to why this happened or
suggestions as to diagnostic or  fix measures?