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 you have got the dohc mitsy engine it sounds like the idle air control valve stepper motor is either gunged up or just shot try cleaning out the throttle body with carb cleaner. if its the hyundai beta engine (black cam cover ) its the throttle position sensor playing up.[]

 

sorry just noticed you said it has a single wire on the throttle body so yours is the mitsubishi engine( the wire is for the idle on/off switch) so definately stepper motor fault.