04 blazer ls, runs and starts fine, during mild/summer weather. temp overnite drops to 35-40, starts OK,but idles rough as h....... til it warms up, then ok??? outside temp today 53 deg. no prob on idle after startup. could this be faulty coolant temp sensor? has new thermostat and intake gasket installed 6 mos ago. has run fine til weather turned a little cool. tks to all,

 

Could be any number of things:
Any difference in how it acts after it rains?
Could be small vac leak.
Could be sticky IAC. Only problem I ever had with iac was in cold weather starts. I assume because of 'gum-up', didnt want to go to high idle.
Could be plugs worn and cant handle richer mixture.