I have a 1990 Lumnia 3.1 that runs great until I shut it off then for about 5 min its spits and sputters?

It only does it when its at running temp, I was told it was the crank case sensor so I changed that, but it still does it. Any suggestions, I just bought the car and they said it ran fine and if it did that then just put a bottle of heat in it. (which was BS)