Well I THINK I may have figured it out............Maybe. I noticed the idle was around 600 in neutral and closer to 550 when in gear. So I bumped it up closer to 800 (where it should be?) and what do you know, the volt meter does NOT drop off 14 even with the lights on! Could it have been that simple, the idle was too low to energize the alternator circuit? I did buy a new negative cable for the alternator to the PCD, since that was the one with the bare cable and corrosion on the alternator end. It can't hurt right?

 

Yup, that certainly could have been the problem all along. And it can't hurt at all to replace any questionable cables.

 

how did you bump the idle? The blade position isn't adjustable, at least without some work to remove the inserts over the adjuster screw. And yes, that could have been it.

 

I guess it had been adjusted before. A small torx bit fit right in there and I just gave it a little clockwise turn. The OEM spec idle is 800 right? Now is that in neutral or in gear?

 

there's supposed to be a pressed-in steel cap over the idle adjustment screw, that has to be drilled out or otherwise forcibly removed. No idea what the spec is. Heck, i dont even know what mine idles at, never pay attention.

 

I have been following your thread hoping for an answer as I have had this same issue in my truck since I owned it. I have tried just about everything (cleaning and replacing IAC, TPS, throttle body, plugs, wires, cap, rotor, new battery, etc.) and nothing seems to make a difference. Mine only acts up when it starts getting cold, usually from October to April. Now that you bumped your idle, do you get a bounce at all? Does your truck hiccup when you first take off on a cold morning? When my truck is warmed up my idle will bounce several times, like the computer is trying to find idle and can't settle on it for awhile. This causes my lights to dim and voltage to dip and rise, eventually settling around 12V, sometimes lower to the point it begins to discharge the battery or even stall out the truck. If I give the motor just a bit of gas it rises back up to 14V and everything is good. I may have to try drilling out the steel shim that is in the way of the idle adjustment, and just manually move it.

Mine is set up the same, might have to remove the insert and make the change. Would like to have this solved once and for all, not as if my MPG is getting much worse or I am voiding a warranty at 155k miles

 

The "idle speed" adjustment is actually the minimum air adjustment and there's a very specific way it's supposed to be adjusted (though I don't know off the top of my head what it is). The idle speed itself is controlled by the PCM through the IAC.

It's possible your IAC is bad, since the PCM would normally close it down to compensate for your throttle blade adjustment and maintain the "desired" idle speed.

 

FWIW, mine idles at 670-700 RPM both in gear@stoplight and in neutral. Digital dash reports 13.7 volts.

 

I have replaced the IAC at least twice along with cleaning it numerous times. It will improve while the PCM relearns the IAC behavior, then it is back to the same thing. Only happens when it gets cold outside, below freezing or at least below 40F. Really bizarre, has done it for as long as I have owned the truck, going on 7 years now. I just lightly tap the gas when I come to a stop to keep the idle up and voltage in the 14V range. It is annoying and can be dangerous, I have had it die on me coming down from the ski hill when I am downshifting going into a corner.... not the time for the steering wheel to lock up and lose power steering and brakes!

I am thinking it may be something within the PCM itself. I know the durangos and some dakotas had issues with the PCM getting too hot and capacitor connections separating causing the vehicles to shut off. I wonder if it is related, but not worth replacing the PCM IMO. I can deal with it...

 

Maybe it's your battery temp sensor? I have NO IDEA how it works it's way into the system though...but since you mentioned it was outside temperature related.