Code P0123 - Throttle/Pedal Position Sensor

I just bought a used Audi A3 Sportback 2006! I still am super excited about it but I am experiencing some issues.
I am getting the code P0123 from the computer which is Throttle/Pedal position sensor A Ckt High Input. If you have had this issue, can you help me diagnose this problem?

Here is some history. For the last couple of weeks I had codes P2293, P0171, and P0222 coming on intermittently but especially after I filled up with gas. A friend of mine thought the issue was the fuel filter and we replaced it today. (I can give some advice on this one if you need it) I cleared the codes and expected the issue to go away. It did not. The codes have cleared and not returned, but I have the new code P0123. I also still have the same symptoms indicating that the engine is not functioning properly.

Current symptoms: the power to the engine is not engaging when the gas pedal is pressed heavily.
My transmission seems to be okay because I can shift to all 6 gears in automatic, sport mode, and manual. As I start to drive my engine seems to be okay but as I continue to press down on the accelerator pedal I do not get an increase in power although I can hear my engine revving up. The rpms do not go above about 4000, but it sounds like they should be higher.

Any thoughts would be welcome.