I am located in Anchorage Alaska, and have an 87 Syncro Westy with a cold.
When the temperature drops into the single digits, the engine hesitates and
stutters.  It seems to be worse AFTER the engine warms up, and the problem
intensifies at around 3500 rpm.  I have replaced the T2 sensor.  I also ran
about four tanks of Chevron Supreme through it, and thought I had it
licked...  until the temperature dropped again.  The gas up here is
"oxygenated" with ethanol, so we have a built in gas dry supply.  This
weekend, the temp dropped below zero and the hesitation returned.  Sunday
the temperature was back up into the "balmy teens" and the hesitation quit
again.  No problems starting, even at the lowest temperature, and this
without any type of pan heater.  Any ideas?  I am thinking this is fuel
system related, either the fuel pump or perhaps pressure regulator.
Something that doesn't warm up significantly with the engine. I have tried
searching the archives, but can't zero in on anything that fits.  Thanks,
John