HELP! On the freeway my car started shaking and it violently shakes on idle, what do I do?

Sounds more like a plug wire. Either popped off plug or coil pack / distributor? If its raining pretty good then it could be watter intrusion again in distributor..? the other end of the plug wire (opposite the spark plug) dry it out with a rag, let air dry. With car off - puts hands on, feel, tug, push, something loose or burnt through. if it just started like that with no warning you should be able to almost see it. Unless water got in. Its in the "spark" parts of the car, follow the plug wires.