sorry for the drawn out story but need the expert advice from the board.

2 weeks ago I passed emissions with flying colors. The interesting thing was that while the guys accelerated on the rollers, i could see a puff of black 'soot' (not really smoke) come out when he hit the gas. This may have been the first time I have seen my car run from the outside, and do to my slow driving habits (driven in traffic alot), figured it may be a bit of carbon buildup or something.

Saturday after running errands half the day and then letting the car sit for an hour, started it up and the exhaust note is noticably different. deeper/muffled sounding and louder. Engine idles a bit rougher these days too, however that has been happening off on on for a couple months.

Car is throwing no codes and is 'slightly' down on power (however it is a 3.4 and is always ).

Does this sound like the cat? O2s? both? Or am i completely missing something obvious? Do cats go bad within an hour of having the car off?

BTW, cat doesn't seem to rattle when hit (i always thought that was the way to tell).

Thanks again for any input.

 

any ideas?

 

dont worry its just a 3.4 and you passed smog if it fails next time trade it in ad get an ls1. or trade it in now and get an ls1