I have a 84 300zx that I have had for 4 years. It will crank like new then after 30 seconds to a minute it will start to idle up and down, smoke hesitate sometimes cut off. But after about 2-3 minutes it will "warm up" and go like nothing is wrong. It actually does better in cold weather. Sometimes if it is cold enough it will go right on but the warmer the weather the quicker it goes into its mode. Any ideas?