Q: p0171, back fires at idle, lack of power and red hot catalytic conterter?

The P0171 trouble code relates to a "lean condition" and applies generally to many makes and models of cars. This simply means the air/fuel mixture is lean meaning that there is too much oxygen present in relation to the amount of fuel present in the system. This can cause a variety of problems, one of which you are describing which is a catalytic converter failure, turning red hot and stalling or loss of power. The catalytic converter converts otherwise toxic exhaust fumes into less harmful materials to expel into the environment. When this is clogged or not able to pass these fumes out into the atmosphere, it creates an enormous amount of heat in the car’s exhaust system as it backs up (think of a sink being clogged). I would recommend having an expert from YourMechanic come to your home to diagnose and repair the loss of power.