I have a 2006 5.9 cummins and I was wondering what is it supposed to idle at? I am new to diesels and I have only had the truck for a month and it idles at two hundred rpm! I should also say that I just recently changed the fuel filter. Before that i did not pay close attention to the idle and it has a k&n filter.

 

The cluster has an issue, a typical failure with your year. Idle should be 750-800 rpms, it won't at 200 rpms.

 

Thank You!