3.8 Misfire.
 

I have a 2000 Buick LaSabre. It has a terrible misfire. When its sitting still and idling, it constantly idles low and then regular, low then regular almost as if its about to cut off. If I slightly press the gas it idles fine. Also when I drive it the car will putter upon take off, but then will smooth out once I get up to speed, when its puttering or when its idling up and down the check engine light is flashing. I've tried to pull the DTC codes but all I am getting is code PO300 Random Misfire. I am suspecting it need a catylitic converter or maybe a tune up, but how can I be for sure? Is there a way to narrow the problem down to something specific? Any advice will be greatly appreciated. My car only has 114,000 miles. Also when it putters I can hear the muffler rattling

Come on guys can't anyone help me??

This forum sucks!!! Its Been almost 2 weeks and no one has even tried to help me with my problem! ! What's the use of having a forum if you cant get decent advice or help when you need it. I am highly disappointed!!!! I am deleting my account. Thanks for nothing!!!!!