i've been having this problem for some time now. every time i fix something on it it runs ok for a couple of weeks and then returns to running bad. oils been changed, fuel filters changed, and has good fuel pressure. cps (crank positioning sensor) has been changed. and there are no vacuum leaks. doesn't blown any abnormal color of smoke. what happens is i will be driving down the road and everythings running fine. i give it more throttle and rpms or speed do not increase. they start decreasing no matter how much throttle i give it. i pull over to the side of the road it idle extremely low. i reve the engine a couple of times and everything returns back to normal. only possible thing i can think of now are the exhaust valve, injectors, and thats it. any help would be greatly appreciated. im not sure what to do next.

 

Any CEL?? If you've ruled out any fuel delivery/pressure issues, and there are no other driveablity/running concerns (surge, buck/jerk, general lack of power, stumbling/eractic idle ect), and you are experiencing a 'dead' peddle, you may want to have a look at the AP.. Accelerator pedal position sensor.. These diesels use a 'fly by wire' throttle position control, using a TPS (throttle position sensor) and a Idle validation switch all mounted as a unit on the Accel. peddle assembly.. What can happen, is that you get a 'drop out' or failure in the TPS or circuit/s and the truck will return to idle under load.. Once stopped it may work fine for some mileage.. Also, check the connections for any bad pins ect.. The AP can be tested, but intermittents can be tricky..Could be a PCM problem as well, or circuits in between if related to the AP position sensor... First thing would be to have it checked for any DTC's for a possible point in the right direction..

......................HP.................