I have an 04.5 C600 that has recently started doing an intermittent rpm fluctuation when at idle (such as at a stoplight). The rpms will surge about 100 rpm or so very quickly (half second-ish). Sometimes the rpms go up, sometimes down, sometimes both back to back. It only does this every once in a while when I'm driving around town, but once it starts, it usually keeps doing it until I stop the truck.

I have changed the fuel filter, cleared out the water sep, and even changed batteries thinking it might be a bad battery causing a voltage problem. Nothing has changed it.

Any ideas?

 

mine does it as well

 

Try dosing the fuel with ashless 2 stroke oil for a couple tanks.

 

My truck does the same. I like to think it is just normal

 

I got the problem diagnosed. Supposedly the fuel control actuator needs to be changed. Does anyone know how difficult it is to do this? The parts are not that expensive, but I'm not interested in an all day project to change it.

 

Its 2 0r 3 torx head screws and one electrical connection. The problem is the screws will seize in the pump and strip out if your not careful.

 

please don't take this as an insult to your intelligence but could it just be the a/c compressor kicking on and off, it will cycle in either defrost mode. cant say mine fluctuates that much but definately noticable.