i've got a 95 elantra. when its warmed up the engine will not idle at a constant speed, it surges up and down. there is a single wire that hooks up to something at the throttle body and if you unhook it, the engine idles at very high rps but doesn't surge. (dunno if that helps) any one got any ideas?

 

if your lantra is the dohc mitsy engine i would take a look at the idle air control stepper motor in the throttle body, try cleaning it out first with carb cleaner and a rag.