Why is my car messing up

Obviously its problem with your fuel to air mixture. It is building up unburnt fuel due to not enough oxygen. This lack of enough oxygen will cause the stalls and the build up of gas will cause the backfires. Heat affects the mixture ratio. A number of detector are involved in the exhaust system and any one of them could be failing. Throttle Position Sensors, MAP sensor, Oxygen sensors, catalytic converter, etc. You should be getting the check engine light coming on also. Any auto parts place can read you the code numbers for free. They will provide more specific information about failing parts.