Why is my engine misfiring?

I hope someone can help me with my car. I have a 2002 ford taurus, 55,000 miles. I was on interstate 95 and my car ran hot. Well, I put water in it and came home to find out I had a hole in the reservoir for water and antifreeze. Replaced that, Got a code reading of p301 changed spark plugs, wires and coil pack. Still has misfire. I have been driving the car since november of 2006 like this because noone around here can say what is wrong with it. I'm a woman also, and they tend to think we don't know how they can gert over on us. I just need some other suggestions as to what the problem could be. When I start the car it vibrates, when at a stop light and take off if feels like it don't want to go sometimes. While sitting at the light sometimes ift feels like the car is going to take off. You can hear the exhaust rattling under my car. Any suggestions? Thnak you very much.