I had a buddy who had a Paccar motor, he was having the opposite response from his throttle, it kept increasing. He took it to the KW dealer and they had him down for over a week thinking it was a throttle position sensor, then he got it back and on his way to CA it happened again. The problem would only happen while he wasn't on cruise so he set the cruise and road out to CA. He put it in the dealer out there and two weeks later flew home and got a different truck from the leasing company.
He later found out that his ECM was losing voltage and it was freaking out the truck. They had research and development guys from KW that flew out there, they replaced the entire wiring harness and everything on it before they finally figured out the ECM was the problem.
Point in all that is, it sounds like that code relates to possible ECM issue from reading the link Jerzy posted, if it's shorting out it might be causing the computer not to read the throttle position sensor which could be resulting in your symptom. Sounds like it's probably electrical to me.