My 04 LB7 is fluctuating in engine RPMs. Not enough to see on the tach, but about 5% engine load on my hyper tech monitor and you can hear the engine change when it is doing it. It has more at idle but it does happen warm, cold, idle or loaded, but it is harder to notice when loaded. I have seen post that suggest Fuel Reg Valve. I did just change the fuel filter but have not seen any results. Any ideas out there?

 

Usually when you have a variance in your RPM fluctuating its going to be the Fuel Pressure Regulator but that causes a lope, just youtube lopey dmax and you can hear what I'm talking about. I doubt your rig is doing it that bad just a thought to look in the FRP there around 220 bucks to replace and they are a pain since there in the valley on the engine if i recall.

 

Yep, fuel pressure regulator.

If anybody's ever seen the fuel rail pressure on a Tech 2 plot when the regulator is bad, you'd see why the idle fluctuates.

 

had same problem in mine and fpr is what fixed it

 

Thank my diesel god!!!!! I've gotten hosed out a couple grand from different mechanics trying to fix my fuel problems. Cp3 pump, 5k worth of injectors!!!! 2 days on this site and I've fixed 3 problems with my truck!!! Thank you all.