I always assumed that it was good for the engine to idle for a few / couple of minutes at start-up, to let the engine RPM settle down.
Right now the temps here in South East Wi range from 17-30 deg. In the morning the truck RPM is about 850 when first started. After couple of minutes it settles down to just below 500rpm.
I am reading conflicting advice on the net, with some experts claiming idling an engine is bad. While others say idling for extended period of time is bad, but there is no definition of what entails "extended period of time", though I assume it means well more than start-up idle, so over 15 mins.
So is it good or bad to let my LML idle for a couple of minutes , until the RPM has settled down?
imho, it depends on what you are going to do with the truck.
In cool (not cold) weather I usually wait for it to idle down (mine trucks have all lived outside, and I use remote start, so that doesn't mean I'm sitting in the truck waiting for it)
You should enable the 'elevated idle' function.
When it's warm, it will do nothing.
When it is cold enough (ambient and engine coolant temp) it will run the idle at 1050 rpm. It also sets the torque converter, fan and turbo to create more heat. This also warms the transmission oil.
If your truck lives outside, remote start and the 'elevated idle' are your friends in the winter.
Remote start will run the truck for 10 minutes. It can only be used twice and then a key cycle is required before it can be used again.
(the fob can be used to extend the first cycle -- but the time extension counts as the 2nd cycle)
There is a bunch more info about 'elevated idle' in the duramax supplement.
(Don't confuse this with the 'high idle'; or 'fast idle' function which is for a different purpose, and needs to be activated manually)
Once coolant temp reaches about 150F, the 'elevated idle will shut itself back off.
Elevated idle is supposed to only work below 32F. This was true on my LML, but my L5P seems to engage elevated idle a few degrees above 32F, although I haven't been able to sort out what the limit is.