The car in question is an S5 NA 'vert. This issue has happened with both the stock exhaust on the car, an aftermarket exhaust on the car, a stock airbox on the car, and an aftermarket cone filter.

Anytime I start the car cold, it runs fine. If I make a stop or two...it still runs fine. If I drive for a long period of time and try to drive again within a few minutes or I make 3 or 4 stops within an hour, get out, and come back to the car, this is the issue I experience...

...The car will have full power for a moment and then...none. If you press down on the accelerator you hear the engine trying to have more power but instead it stutters and bogs down...even worse than limp mode. I mean it litterally feels like you have about 5HP.

Any thoughts?