I am sorry that you have not been helped yet. I just came online and saw your question
Ok, yours has a fly by wire throttle system. There is a sensor on the gas pedal that converts the amount you press the gas pedal to voltage readings which is sent to the engine control module and then to the electronic throttle body.
There is either a fault in the APP(accelerator pedal position) sensor on the gas pedal or a fault in the electronic throttle body. They both will need to be tested, which requires a full function scan tool to determine which is faulty, and the faulty one replaced and programmed
The electronic throttle body lists for $732 and is about $180 labor to install
The APP sensor lists for $274 and runs about $60 to install.
So with both being pricey, you do want it tested before any parts are replaced
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