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human
ELI5: Why does my car idle at a higher rpm when its cold?

When I started my car this morning it was -15F and my car was idling at 2,100 rpm then ~10 minutes later when it was warmed up it idled at just under 1,000 rpm. Does the car purposely increase the idle speed to help warm up the engine or is it a mechanical thing that just happens on its own? Its a 1995 honda accord if that helps.
gpt
It's not actually to warm up the engine for the oil, it has to do with combustion.  The requirements are fuel (gasoline), air, and a spark - all under pressure in a precise ratio and timing.  This process happens ideally at warmer temperatures (the "operating" temperature) as this is where the fuel vaporizes naturally.

When it's cold, combustion requires much more fuel in the ratio because it does not sufficiently vaporize from liquid gasoline into a gaseous form (liquid gasoline, for the sake of this discussion, does not burn).  The problem is, too much fuel through the engine at a low speed bogs down the engine as the unburned liquid fuel will kill the spark and cause it to stall.  The RPMs are bumped up to push this fuel out more quickly until a more desirable temperature is attained.  Once warm enough, the fuel vaporizes as it should, the computer dials back the fuel mixture (or the carburetor opens the choke) and the RPMs can come down.

Source: 10 ASE certifications and 7 years as a mechanic to get through college diagnosing/repairing smog and computer systems.