I have a 2001 Jeep Grand Cheokee and it is overheating when I idol and when I idol the heater is not blowing cold air. It will blow warm air while I am driving down the road. What do you think could be wrong with it?

I think you have more than one problem here. The overheating at idle could be the electric fan (if fitted) is not cutting in.
Second, the changing heat output can be low water in the system or something, heater rad, is blocked or restricted.
Get help from someone who knows cooling systems. Always use correct coolant/antifreeze regardless of location. Antifreeze mix affects boil point.

Check the cooling fan motor and of course the fluid level. If the temp is changing thru the heater it could just be low on coolant , leaking from ? Two wheel drive have an elecrtic cooling fan only, make sure its spinning up when temp is 3/4. If not its probably the fan motor. Can be checked with a test light .