I would suspect the stepper motor or the base idle adjustment. I had really bad hoses on my RRC when I first got it but it still idled fine. I have the funky idle sometimes it seems it wants to stall when I put it in gear. Ive done lots to this truck and I have not gotten it to run as smooth as my other Rover. I imagine the issue is hidden deep within the bowels of some electronics that I dont care to bother with.. Nice looking trucks youve got.