rough idle.....im stomped.....

:uhoh: 2000 firebird 3.8, its acting worse than before I replaced the coil packs.
i got all the wires in the right other, I got spark on the coil packs and on the plugs, I got no leaks whatsoever. The only codes that come up are p0420 which I know what it is. Its the catalytic converter, I put a high flow one, and ever since its giving that code. The other is p0440, EVAP vaccum leak/clog condition or something like that, so I dont think the A/C has nothing to do with the rough idle. I also checked the gas cap, but even though the leak is from there the change is not that significant. Please guys, I need your input on this...... thanks!!:uhoh:

ok, surfing the web, I googled catalytic converter..... and the symptoms that my car has are very similar to the one's of a failing or even plugged CAT. Now my question is, Do CAT.'s fail just like that or do they do it gradually?

Please help, I just came from a friends house that is maybe 30 or 40 mi. away and it almost chugged a whole 1/4 of gas round trip.:banghead:

A clogged cat will kill driveability 'cause the engine can't breathe and have no power whatso ever, and sound muffled at the same time.

I changed the CAT. this morning and its seems that the problem went away:frown: , sort of, I dont know, I think its in my head now, but hopefully its fixed.

could be leaky injectors? pull the plugs and see what's going on.

If it is the cat, youll know.

MY question is, have you put ANY alternative fuel or anything besides gasoline with up to 10% ethanol in it?

If you put something that slows the burn time of the fuel down, you can actually melt your honeycomb in the cat(s). Happened to me with my ford when i had it. Also, is it a 3rd party cat? Universal cat? If there is an air injection system the cat might not be made for that, it could really overheat and consequently melt it.