I know exactly what that is.
Your idle control valve is stuck wide open or you have a major vacuum leak.
The reason it fluctuates like that is because your computer sees that your rpm is too high as compared to what the TPS value says it should be reading so it shuts off the injectors for a few revolutions and then turns them back on.
Give your ICV a whack with the handle of a screw driver and see if it drops. Also, if you (or someone) turn on your ignition you should be able to feel the ICV vibrate in your hand. If it's not........