Happy New Year, Everyone. Looking at a '91 D350 for a friend. It doesn't want to trottle back after warmed up. He just bought it and says the previous owner had his employee turn up the fuel, but admitted they didn't know what they were doing. After cold start, it will throttle back to idle, but after warmed up, it stays at the last throttle position when the trottle is released. Any thoughts, or suggestions? Thanks