1999 F450 7.3 power stroke
 

I have a problem with my powerstroke not reving up upon start up. It starts fine and idles; when you try to rev up the rpms it does nothing. After a couple of minutes of warm up it revs up and you can get the rpm's up on the motor. I have no codes on the motor. I have replace icp, cam, and ipr sensors. Any advice would be appreciated.