I have a 2010 Elantra and noticed after I start it when it's cold the rpm is about 1800rpm but doesn't drop. I never really payed attention on this car but my other cars would drop after a minute or so. Is this normal on the elantra or is something wrong?
In cold weather conditions, the ECM (aka: "the computer") will run the engine richer (fuel) and at higher RPMs for the purpose of getting the catalytic converter to reach proper/optimal working temperature sooner rather than later. It should gradually drop the RPMs thereafter.
The ECM monitors air flow and temperature thru the MAF sensor (located at the air intake duct) and engine temperature thru the coolant temp sensor, CTS (located in the area above the engine/trans joint; actually, inches away from the MAF sensor).
In winter weather, my '09 Elantra idles high on startup for 1 to 3 minutes. Our newer '16 Tucson, idles high for 30 - 90 seconds. They both feature different emission control technologies.