1994 Nissan Truck at idle my truck cutts out and sometimes

while im driving it if i come to a stop my rpms just drop strate to 0 and the truck well shut off... sometimes even when im trying to turn... it acclerates perfectly fine but if im stoped and in park it well kind of idle... sometimes rangng from 1000, to 500, but if i give it gas while in park and then take my foot off the pedal it will drop strate to 0 again and normaly stall....