Houman

I got a cat back exhaust about three weeks ago because the original cats were rattling and now my new cats are rattling too! they tell me its an engine problems running hot. the car is idling rough but no check engine light.
I'm going to pull out the maf and clean it but do you guys have any input on this?

AMS Performance

you have 4 cats, Are you sure you replaced the right ones? Magnaflow cats are Ceramic core, you should just get some metal core cats.

MarcusF

A "cat back" exhaust is after the cats. Did you get new cats, or a cat back? If you got a cat back, your old cats are still rattling.

If you got new cats, did you get new O2 sensors? Bad sensors can result in either a rich (ruin the wash coat) or lean (overheat the cats) condition, but they shouldn't rattle this soon - even with bad sensors. I'd look to see if some part of the exhaust is touching something else and making noise. AND replace all the O2 sensors w/Bosch universals.

Houman

i got new secondary cats with the setup. its only a coulpe of weeks i know!
i didnt replace the o2's since anything to do with emissions will trigger the check engine right of the bat and its not on! i did clean the mass air flow sensor and the car does run smoother at idle now but i got a set of plugs and wires on the way since its overdue for some time now. you guys think the metal cats will solve this? i'm ready to bore the suckers out and let if flow since i wouldnt want to replace metal cats later either! I'll plant a tree somewhere to keep a clean consciense about the emissions!

OPALW208

i have the stock secondary cats w/ resonator off my 01' CLK55 for sale. let me know. i have no use for that section of exhaust anymore.

AMGMB

OPALW208 are your cats off? and or whats your set up just wondering?

OPALW208

cats off, resonator off, muffler off.

i'm running dual straight pipes to quad tips =)