19Suburban99

I have a 1999 Suburban and during the winter, I notice that when the vehicle starts cold in the morning, it will rev for about 5-10 seconds around 1700 rpm's and then drop down to about 1100, and then once put into drive drop to about 750. For the past two weeks I notice that when I start it cold in the morning, the engine immediately begins to idle at about 800 rpm's without any type of surge in rpm's (i dont know the purpose of the surge, but I know mostly all gasoline powered cars do it on a very cold start). Any ideas what could be causing the engine not to intially have a higher idle? could it be the engine thermometer?
Please Help!