Low idle speed

[Stevie Callaghan]

Hi,
I have a 406 2.0 auto 2000 V. It has a problem with its idle. It wont idle above 500-600 rpm and is constantly nearing stalling because the lights e.t.c dim and brighten up again with a blip on the throttle. It frequently stalls when cold and when coming to a stop. Throttle cable and clips all present and ok. Could it be a stepper motor? And what does the stepper motor actually do as i've run it with it disconected and it seems a little better (if warm).
I'll be thankfull for any ideas.