robib600rr

Hey guys I was wondering, i own a 97 Civic Coupe SI (canadian version SI) and for some reason the heater seems to only want to kick on when im above 1500rpm's or so in the colder weather, If my car is just idling at 800rpm or so then the heater doesnt seem to want to work, just spits out cold air unless i put my foot on the gas while in neutral. If anyone could give me any ideas, I also had a few problems this summer with my car overheating, I never changed anything, yet sometimes it overheated sometimes it didn't, but seeing as how winter is coming, it would probably be a good idea to get this fixed asap, any help would be greatly appreciated, thanks to all