Idle increase

[NOMOGAS]

my 05 dodge cummins 6m 25k miles idles at 800rpm after 3-4 minutes cold or hot will increase idle to 1000rpm i tap the throttle it goes down but comes up again in a few minutes. whats the deal.

 

[99Supercab]

Its normal, thats the high idle feature. Supposed to help heat the engine up quicker if I`m not mistaken.

 

[TSpecht]

It does that mostly to help prevent washdown of cylinders from uncombusted diesel fuel. Once it's up to temperature it'll also bump the idle up to 1000 RPM for a couple minutes at a time to help prevent the engine from cooling down too much. Diesels are too efficient at idle and in cold weather, this can lead to a decrease in temperature and some side effects. It's best to not idle a cold engine (in fact, warm engines too) longer than a couple of minutes. Bottom line is it's behaving as it should.