idle problem?
 

I have a 92 f-150 flareside w/302 in it. My problem is that when i turn on my air or defrosters the truck will not idle up, instead it will start to die out (loose rpm and voltage) and eventually shut off. It will stay running with my foot on the pedal though. Also in the morning when i start it up it idles up and down from 1000-1800rpms, until it warms up then it stays around 500rpms. I do need a tune up i know that much, but is there any specific area i can look at for the problem im having.