I ocassionally drive the car in sport mode. I would accelerate and the car would go into fourth or fifth gear. Then, the car would start stalling as soon as I stop pressing the gas pedal or start applying the brake. At that point, the engine would make loud noise as well. What is causing this?
It is possible that the noise and "no power" symptom you experience is the exhaust pressure in the turbocharger of your engine being released. In some cases, an excessively rich mixture of fumes in the exhaust is ignited causing a "popping" sound. This is actually combustion of the fumes, not unlike combustion inside the engine. If your vehicle is still under warranty, you might want to discuss this behavior with your dealer to determine if this is a "normal" behavior with this vehicle in those circumstances. Also have them check for any problem codes. If your vehicle is not under warranty and you want to have this checked outside of the dealer, a certified professional from YourMechanic can test the vehicle and diagnose the stalling issue at your home or office.