its a stock 93 S, k last night i was trying to think of some cheap things it could be and my bros old 240sx did the same thing once and it was the pcv valve. so i go and pull it out and it breaks as it comes out so i buy a new one, put it in, and start it and it runs like new drive it all last night its fine drive it all today and its fine then i just went to leave it its doing it again!!!!!!!!!!!!!!!