Forced air natural gas furnace?

I have a furnace that has one of those blowers that pull the gases from the combustion chamber and pushes it out the chimney. Every once in a while, it will cycle on and off repeatedly for like a minute or two. And then stop. Then when the thermostat kicks in the heater, it comes on like it should and works. But after a while of sitting, it will do it over again. I don't know what that fan is called.