Rough idle and charging issue.
 

I am posting this for a friend who has a 2004 Dodge 2500 4x4 6sp. The truck has a smarty Jr. He just installed 2 new batteries and a alternator. About 3 weeks ago he noticed a intermittent rough idle for the first 2 minutes after start up. Also during the 2 minutes the voltage gauge read around 12 volts and then jumps up to 16 volts. Once the gauge reads 16 volts the truck will idle fine. But as soon as he shuts the truck off it will repeat the same procedure for the the first 2 minutes. The truck had a code that read map sensor voltage too low. He cleared off the code with is smarty and as of now there aren't any codes. I cleaned the map sensor with some carb cleaner, but I'm not sure if that has anything to do with the Map code staying off.

Any help would be nice. Thanks!

The drop in voltage probably comes from the grid heater. Mine stays below 12-13 then rises after a few minutes depending on the outside temperature and whether I'm starting from cold or restarting a warm engine.

That said, I have heard that the drop in voltage may cause other problems, like weak flow from a failing lift pump.

Does you bud have a pressure meter or can he borrow one to check?

He doesn't have a fuel pressure gauge. I'll tell him he needs to check the pressure. What should the pressure read at idle? I called another shop and they told me the same thing about the grid heater. I also got in my dad's 03 and his did the same thing. So, the voltage issue is solved. As for the rough idle, it will lope for about 2 seconds and pick back up.

Both issues are the normal operation of the grid heaters. It puts a big electrical load on the system.