2004 elantra GT revving itself and stalling
 

OK, about 80k on this car, and other than the notorius elantra
headlight issues, this is the first problem i've had... It will rev
itself, especially when I come to a complete stop, sometimes
intermittently when at rest, anywhere from 1100 rpm all the way to 3000
rpm-- a tap of the accelerator usually straightens it out...

what does everyone think? O2 sensor? If so, how do I change it? I'm not
an automotive idiot, just don't get under the hood of newer vehicles
often (I have 3 ice cream trucks, all 70's era chevy panel trucks)---
but I need to get the Hyundai running right, and want to do it as
cheaply as possible...

Thanks in advance folks.