Cold Idle Problem

I have a 89 allante. it has the 4.5 non- northstar. im 18 and this is my first one, i have always wanted one and now i have one! sometimes when the car is cold the idle will sit at 1000 rpms than drop and almost die but it is systematic. i will do the same thing 1000 almost die 1000 almost die. until it hits half way on the temp gauge. Any help would be greatly appreciated!