I'm back. It's a 2000 Mustang 3.8 Manual Non-ABS. I have a bit of a problem and mystery concerning my Mustang. I changed the original air-intake for a K&N cold air-intake and new idle control and about to put a 2004 Ford Mustang throttle body and cable on my car. Now when I am driving down hill (Interstate highway) on my way to work, I usually like to put the car in neutral and coast gaining a speed of 80mph. It's around this time that the RPM's will start fluctuating (up and down) between 1000 and 500 before falling below 500 and then the car dies, a complete fuel cutout. Quite dangerous at that speed. I have to feather the gas to keep the RPM's up so it does not die. Now then, at a complete stop or traveling around 40mph in neutral slowing down, there is no issue. Any ideas? Feel free to ask me questions. Note: I have no check engine light.