Cold Start Sputtering & P0420

[OneEightSeven]

Hello,

Car: 1999 Camaro 3.8L Automatic

A week ago or so I threw a SES code so I had its scanned as P0420 (catalytic converter efficiency) and then it went away (was not cleared). Now it came back again and this morning when the car started it sputtered until I put some gas in. Basically it sounded like a small v8 for about 20 seconds. When i was ready to leave work it did it, kinda but just sounded like a vibrating idle, not nearly as noticable as in the morning and went away without me doing anything within like 3 seconds.

In your experience what are the usual suspects for this kind of issue? I will be taking the car into a shop within a day or two and want to know what to expect so I dont waste time. This is a new mechanic as I just moved to Houston and don't want to be replacing all kinds of crap for no reason if the mechanic is not up to par.

I've been thinking along the lines of these possibilities:

1. Bad wires/plugs, not sure when they were last replaced?
2. Bad cat or o2 sensors or MAF/IAT sensor?
3. Coil packs?

I don't think it's a vacuum leak or oil leak into exhaust manifold seals (i forget what autozone quoted it as, i think thats what it was) as I believe a vacuum leak would be a pretty much permanent sputtering at idle and I don't seem to be losing any oil nor do I have any weird exhaust coming out. (or am I wrong in my assumptions?)

I did have a sticky lifter situation a year or so ago, but that was fixed by running new oil through the car a few times and highway driving (the car was parked for a while before hand).

Any input would be greatly apriciated. Thanks!

[bluovlh8er]

Re: Cold Start Sputtering & P0420

if it says that your cat is bad why would you put plugs and wires in? how about getting a new cat???????????:slap:

[kristen]

Re: Cold Start Sputtering & P0420

wow i can't believe that your asking this lol. it's the cat. and not that doesn't mean a small furry critter that meows and pees in a litter box

[OneEightSeven]

Re: Cold Start Sputtering & P0420

if it says that your cat is bad why would you put plugs and wires in? how about getting a new cat???????????:slap:

Because that error code means that that the O2 sensor behind the cat is showing bad readings and thats one of the possible causes of the error? I found the autozone printout:

1. Catalytic Converter defective (Failure possibly due to #2, #3 or #4).
2. Engine misfire or running condition.
3. Large vacuum leak.
4. Engine oil leak into exhaust-valve guide seals, piston rings.

I realize the cat could just be bad, I was just looking at possible causes, especially due to the cold start misfires causing the sputtering.