99 Si misfire
 

Yes, another mis fire thread.

I have a 99 SI automatic, and i'm geting a random mis fire on all cyls. And i think the cat might be clogged - the car is slow as hell...

but would a clogged cat give the 02 sensor readings that woudl then somehow cause a misfire? I'm aware that a bad 02 would 'feel' like a misfire, but wouldn't the computer sort of 'know this' and not report a misfire?

Thanks,
Matt.

why not just take it to a qualified technician and pay him to fix it?
I wouldn't just go replacing parts (like the cat or o2 sensor), b/c that will be more expensive than paying a mechanic to fix it.
Random misfires can be tricky to diagnose...especially over the internet.

Catalyic convertors never go old. They is always a cause for why they go bad (except of course if its an internal problem)

Proper way to test a clogged cat is either a thermo gun or a exhaust pressure test.. which i doubt you can do...

I'm with lenny on this one, bring it into the shop. they'll properly do a tune up and call it a day