I have a 2006 2500 at 213,000+ miles with 4" duel stacks. I have a twister muffler 2' off turbo then off set to a Y pipe then up to the sky. Like a big rig. Sometimes at a dead stop my idle will hover around the 250-300 rpm range. Also the tachometer will jump from there to 1000 rpm and then jitter around In that area. In park or drive makes no difference. I'm not a trouble shooter type of mechanic. I'm more of a If I see it fall off and skip down the road I can put a new one on kind of guy. If someone could point to me in the right direction I sure would appreciate it. Thank you.

 

Sounds like injectors/fuel delivery problem- when is the last time a fuel filter was done on it? Injectors been replaced? Do you have a rail pressure gauge? Any excessive smoke when driving/white smoke? Oil level good and not smell like diesel? Should idle about 500-700rpm

 

I change the fuel filter at oil changes or sooner very slight black smoke no white smoke don't have the rail pressure gauge and it's idling right now about 350.

 

Oil levels good and it doesn't smell like dieseland think I hear the fan clutch kicking in. cold sitting in driveway.

 

Have injectors been done before? Does the motor sound like its stumbling or does it sound normal and rpms are reading down?

 

The tach issue is very common there is a cracked solder in the back. Just ignore it or remove and do the repairs posted on youtube!

 

I've had the number 5 injector replaced by Dodge along with the valve cover gasket. The engine sounds like its idling it 250 to 300 when the tachometer is actually showing that.

 

When it's doing that pop the hood and wiggle the injector harness plug ins on the valve cover! If that doesn't fix it take it back to the dealer sounds like a defective
valve cover gasket/harness.