1998 Chevy Lumina Will NOT idle

I have a 1998 Chevrolet Lumina. It has a 3100 and it just refuses to idle. In the mornings it will run fine, or after it hasn't been driven for a while. But as soon as it gets warm or it refuses to idle. I went about it the wrong way and started throwing money into it randomly. It has a NEW: EGR valve, MAP sensor, IAC valve, TPS, PCV valve, plugs and wires. I was told it could be a leak in a vacuum but I have checked a few times and really found nothing. It has gotten so bad that you can't even go through the window at a bank or fast food place with out it bogging down and back up. When it does this it drops from 300 to 2000 rpm, and if you let it 99% of the time it will shut off. It drives like a dream. It has just gotten so annoying I don't like to drive it. It is easily provoked at idle by a heavy electrical load as well, Rear defrost of automatic headlights kicking on will usually make it happen if its not happening all ready.