Urq Suddenly fast idle speed it's cold outside

[R1chT@aol.com]

After driving home last night, my idle speed is now about 2000 rpm after
warmup to 190 F as measured in coolant reservoir,  duty cycle measures 68 to
75 % on fluke DMM note this may be inverted from the way it's measured on
other meters. so it could be 25 to 32 % I forget which way is richer. Haven't
tried to change idle mix, I don't have my 3mm allen wrench (was stolen). My
thought is possible  ice on the airsensor. What about a vacuum leak? or other
possibilities. Currently about 0F outside. This is your puzzle for the day.
Thanks for your comments. 

-Rich 
Concord NH
'83 TQC