The vessel has about 700 engine hours. It has been very well maintained by certified mechanics for over the seven years I have owned it. The problem is that the port engine will not respond to the throttle (most of the time). It will go up to 1,000 rpms by moving the switch on the side of the helm station. It will run fine. It will increase RPMs by pushing the throttle forward and leaving it there for a few minutes. It will increase, but goes right back to idle. It does not cut off, and runs very smoothly at idle. The Cummins dealer has run a computer check and did not find anything wrong. They suggested I have the fuel injector pump inspected. I did have it inspected and they recommended it be rebuilt, and I did that. It was put back on, and the engine ran great for about 15 minutes. Then it reverted back to not responding to the throttle. We have moved the following sensors from the port to starboard engines, and nothing has solved the problem: Computer, crank shaft sensor, cam shaft sensor, throttle control sensor, engine control modules, oil pressure sensor, Changed fuel filters, Checked the electronic governor activator, and the rack positon sensor. Any suggestions? I have spent over $5,000 and no one seems to have a clue as to what to do next.