When stopped in traffic my truck (06 auto) changes rpm, you can hear it change tone as it sounds the rpm is lowering but the tach doesn't move it stays right at 750. It has been doing this for a while and before any mods. I noticed my friends PSD does a similar thing. Is this normal? Driving my truck is flawless. I am fairly new to diesel and am used to a gasser keeping one exhaust tone while idling. Thanks

 

You sure it's not from the A/C clutch engaging and disengaging?

 

A/c cycling or Grid heaters??

 

Could it do it if my ac is not running? If so that could be it, from the outside I hear a slight click when it happens.

 

Do run some kind of pressure box?

Andy

 

Remember, the a/c compressor works while in defrost mode as well.

 

Does it only do it during cold outside temps?

If so, I'd bet it's grid heaters.

 

100 bucks says your a/c compressor is cycling, every vehicule with a/c does this, you'll also notice a power loss on smaller hp engines.
Hope this helps some

 

No pressure box and like I said it did it stock. Maybe it is just the A/c it does it warm and cold, maybe a little more when cold.

 

Do you run the defrost? A/C shouldn't be on unless in a/c mode or defrost ( any position between floor and defrost runs it too)

 

Also, if at the same time you hear the "click" you also see the voltage gauge drop then you know it is the grid heaters.defrost-a/cgrid heaters it's gotta be one or the other.....