low rpm stalling

Hello,

I seem to have a problem that happens about half the time coming to a stop sign or a traffic light. As I slow to a stop it stalls..

Is this a transmission glitch or an idle that is too low. That said, it normally idles at about 500 rpm, which seems a little low to me. Is there an adjustment screw or is this one of those "do not touch" emissions related things?

Thanks for the help

Hotshoe