idle drop..97 ford explorer sport

Hello,

I am having a bit of trouble with my Explorer. At start up the idle jumps to about 3,000 then drops back to 700'ish. I can live with that. The major issue though is at night with lights on, fan on, radio on, and at a stop light. The idle generally sits at 500 when stopped. During these occasions is seems ot be having trouble and wants to drop more and everything dims and the enginge begins to sputter. Then something clicks and she comes back. Only to do it again and again till I am able to move. If I leave a little room and can let it roll it doesn't seem to do it. A little gas and it stops. It does happen in the day time as well but not to the same extreme.

Any ideas?

Thanks for your time...

LWA11