We had 1 2004 EGR model with a similar problem. replacing the throttle position sensor would not solve it and needed the harness from the TPS replaced. I cant remember how far it went but i believe it was most of the way to the body controller.
ive seen the same thing on dt466's in gillig transit buses. typically the only fix was was to change the harness from the pedal all the way to the ecm. you may find the shielded wiring cut somewhere.