I have a 2002 3500 5.9 diesel with 279000km on it. This truck has a idle that goes up and down truck runs fine besides that. I have replaced the vp44 injection pump the lift pump and the boost sensor. On eweird thing is when the truck is shut off the boost sensor is still reading 14 psi. The truck was bought used and doesnt perform like there is a chip in it but not sure that's my only thought on the boost sensor. Any thoughts would be great. Thanks

 

there is also no codes

 

Do your dash lights dim when the idle goes up and down? Are you in a cold climate? It's most likely the intake air heater cycling on/off - it draws something like 60 amps and turns on when outside temps are around 40ish degrees iirc.

 

No i'm not in a cold climate. I hook the modis up and the intake heaters are not coming on the truck can be hot and it still does it. dash lights stay the same. I know what your talking about with the lights dimming out though they do when i first start the truck. Thanks for the thought though.

 

Try cleaning the maf sensor or replace it?

 

a 2002 Cummins doesn't have a MAF (mass airflow sensor) is does have a MAP sensor, located on the drivers side close towards the rear, just behind and above the lift pump IIRC from my old truck