engine surges at idle

i've got a 92 civic DX sedan, with a D15B7, when the engine warms up it will surge with no load on the engine. if i turn the headlights on or the heater fan on high it stops. i have replaced the idle air control valve and cleaned the part under the throttle body. does anyone have anymore suggestions?
I'm a little bit new to these cars, but I remember reading something about an electric load detector, or something like that. I don't know if a 92 DX gas one, but I'm pretty sure my 96 DX has one. I think it is either in the fuse panel by the battery, or under it, if that helps at all. Usually, though surging is an indication of air getting in where it isn't wanted, like an intake gasket leak, or a vacuum leak. Hope I'm helping.