Will a broke up and rattling cat cause the car to idle really rough? I know that it can make your engine lose some power and not drive the best it can, but my car idles terribly and when its idling bad, you hear the cat really loud. Would gutting it maybe get me some normal idle back?

I have the same thing happening to mine. The only difference between yours and mine is the year mine is a 89 but mine doesnt idle rough but when it idles at around 500 you can hear the cat rattle loud....

No, a bad cat or exhaust won't make your car idle funny.

The irregular idle makes the car shake or vibrate and thus shaking and rattling your exhaust system, which may have some loose parts i.e hangers or heat shield.

You'll find with a good smooth idle the rattling (well most of it unless you've got something under there that needs tightening or moving apart) settle down quite a bit or be eliminated altogether.

Fix your rough idle.

P.S Guys, check your heat shield above the cat you may have lost a bolt or two and it's making contact with the cat or it may have rusted and fallen.

im no expert, but my new exhaust did this with new hangers on my suburban after my cam swap... I thought it was just the addded power...

nope, that jackass had my 3 & 7 cylinder wires crossed, So if you just messed with your wiring, I would recheck it! then look at the exhaust system. my truck idled like **** too...

It sounds like the honeycomb structure inside your cat has broken up into chunks. You'll have to replace it, gut it, or straight-pipe it; that'll get rid of the rattle.

This probably won't fix your rough idle though.