BlownBB6

I have a supercharged lude. Occasionaly (maybe once a week or twice) , when i start the car the idle will instantly drop after it starts and the car will die. Sometimes if i hold the gas to like 1500 for about 30 seconds the idle will normalise itself. If i just tap the gas before it dies it will rev but then drop right down again and die. if i hold the gas only slightly just at about 4 or 500 rpm it goes really spiratic. it jumps to like 1200 then back down to 400 and so on.. im just curious what would cause the car to do this only on occasion? most of the time it starts right up at the flick of a key and is perfect.