From what I can tell it could be 100 possible problems and I couldn't find anythung saying what usually causes these codes on a monte Carlo. I also don't know if I should take my time to solve the problem or if I should just pay the extra money and take it to a shop. It's a 2003 monte Carlo ss and it was driving fine until it started having misfires when I accelerate and then the check engine light came on. It only misfires when I accelerate and it only does it half the time. Where should I start? And how much will it cost? Thanks for the help.

 

The tricky part about multiple misfire like you said is that there are a ton of different causes. Its not like some codes where there's only 1 or 2 possibilities. Because of that, its also impossible to say what it would cost to fix. Could be simple - could be multiple things.

The big thing to be careful of with DIY is shotgunning fixes at it without thoroughly figuring out the cause. Ive seen a lot of people post on here through the years that they replaced these 10 things and it still does it - thats because they're just randomly replacing parts in the possible cause list rather than diagnosing.

Do you have a obd2 scanner than can read live sensor data? At least to me, its a helpful tool to narrow down the cause. The computer collects bunches of live data, so being able to capture that and record it while its happening helps narrow things down.

 

I do actually. Thanks for the idea, any clue on what I should be looking out for though? I'm really a novice at cars but can't learn without doing.

 

Not sure how many you can log at once, but Id try to capture the major fueling sensors - map, maf, front O2. Then Id also capture pcm outputs - stft / ltft, cylinder misfire counter, misfire by cylinder (to see if there are any patterns).

You're trying to get insight to what the pcm is seeing - the O2 code somewhat points you in that direction. The pcm has a wide range of adjustment, so something is so worn / broken that it can't compensate enough to run right (vac leak, fuel pressure low, etc).

You also want to drive it around to see if there are any patterns - is fueling OK, no missing at cruise - but both are a total mess under acceleration. What about idle, etc. Does the O2 issue always happen the same time as misfiring?