Hard starting

I have a 1999 chevy blazer with a 4.3 v-6 that will not start easily in cold & damp weather. When I spray some starting fluid into the throttle body it will start up and run fine.Is there a sensor for cold starts that might not be working properly?

Yes, the engine coolant temperature sensor (cts) tells the engine computer the temperature of the engine. The engine computer then sends a rich fuel/air mixture signal to the engine. When the engine is starting, and when cold, it needs a richer (more fuel) mixture. The cts may be telling the engine computer lies.