1990 Buick Century Engine shakes

I'm answering my own question. I replaced the catalytic converter, it was broken inside and that caused the rattling. The engine was still shaking though. Then I checked for spark and found no spark from the 3-6 coil. The coil tested good, so then I replaced the ignition module and that fixed the shaking problem. I didn't have to buy the ignition module, it was a part saved from five years ago, when a lot parts were replaced in a trial and error desperation.