Engine idle just started to get a slight fluctuation, the tac dosen't move, that is how slight it is but I can hear it when the truck is running while standing outside of the truck in the garage. When driving there is no miss. I was wondering if this could be an indication of a FCA { fuel control actuator} starting to go bad? It is my signature truck, 2006, 5.9 with about 150k on it. To my knowledge the FCA has never been changed.
Any advice would be appreciated, thanks.

 

I have no idea, but my for about 2 years or so, my 2003 has often idled up/only dropped down to 1100 and stayed there when kicking in the clutch or sitting at a red light. Seems to only happen after it's good and warmed up/driving about 20 minutes or more.

 

Thanks for the reply. Mine is only a slight rpm difference, maybe 400-500 rpm, and only at an idle. Just changed fuel filter just to make sure it was not the problem no difference. Start with the easy stuff first. Runs great down the road just have to wait and see.

 

You aren't just having the grid heater cycle, are you? Mine will make a bit of engine sound change, as the load from the alternator varies.

 

Yup, you will have different things turn on and off while idling, that changes the rpm.

 

Thanks for the input guys. I was thinking about the grid heater also. I will put a volt meter on the battery and check for drops. I will bring the truck up to normal operating temps. first. The truck when warm does the fluctuating idle after the engine temp. is up. I keep the truck plugged in during winter months 24/7 have done this for several years. Maybe the grid heater is worn out from being plugged in for those years/months. The outside temps have varied from -18*to plus 40* , I need the truck ready to roll in case of a SAR call out so I can get to the S.O. warehouse and pick up a county' rig.

 

I thought the grid heater only was activated with the key and there was some other sort of oil pan heater that operated by the 110 ac plug, or am I wrong?

 

I think you are correct. The plug-in that is for 120v is probably a block heater.
I will try to disable the grid heater after the truck is warmed up to see if there is a difference in idle. I'll have to do a search to see where the grid heater is plugged in at.
Thanks again.

 

You will generally see the volt meter move shortly after the grid heater comes on or off, if that is the case.

The grid heater (actually 2) are heating elements mounted between the intake horn and intake manifold. The engine computer activates them via two large relays when intake temp is below a certain set point and vehicle speed is low (below 25 if I recall correctly).

The 110ac heater is just a heating element in the coolant passage, mounted in one of the freeze plug holes in the right side of the engine. The engines ship from Cummins with the heater element installed, however the power cord is usually an option from Dodge (or aftermarket). No thermostat or ECM control on the block heater, it is just a heating element and a cord.

 

What gets me is the grid heater comes on every time you start up (in supposedly under 65 degree temps) in cold weather, even if the engine is completely warm and you only stopped for 2 minutes at the convenience store. It's easy to see it working via the voltmeter, the lights slightly dimming and the heater fan slightly slowing each time it kicks on.

 

Yeah. There is an intake air pressure/temperature sensor on the air pipe from the filter box, and another in the intake manifold.

I don't know which sensor, or combination, or what threshold it uses.

 

Thanks for the info. The reason I think I have a problem with my grid heater is that I have never heard this rpm changing before after the engine was warmed up. Might be a different issue but the truck runs fine going down the road.