glenwilliamson

I have a 2000 Chevy Cavalier that is misfiring. It doesn't seem to be so bad when it's warm out. But as the outside temperature gets colder the misfiring gets worse. I'm just looking for some ideas to check before I take it in. I have replaced the spark plugs and spark plug wires.

Any advice is appreciated

Thanks
Glen

Jiyu

Cold air is dense; hot air is thinner. If the engine is delivering the same amount of fuel to the engine regardless of the temperature, the engine will run leaner in cold weather and richer in hot weather. This is because the air/fuel ratio changes: less air for the same amount of fuel when it's hot outside; more air for the same amount of fuel when its cold outside. So, when it's cold the engine runs lean; when its hot the engine runs rich.

Of course, modern cars have all sorts of gizmos that automatically compensate for changing air temps.

To find out what's going on with yours, go to an auto parts store that can hook a scanner up to your car (most do it for free) and see what codes it throws. (Or buy a cheap scanner, they're handy to have. They plug in beneath the steering column.)
A vacuum leak could be one problem. Look for any potential leaks or cracks in any of the hoses leading to the throttle valve, throttle body, etc. (Check out some YT videos on the subject.) Vacuum leaks make the engine run lean.
Wouldn't hurt to clean the IAC (Idle Air Control Valve), but it's kind of a pain to get to.
Clean your MAS (Mass Airflow Sensor) and throttle body. It's very easy to do, see YT for videos.

oilcanhenry

Likely your coil packs are bad.

372nww

The misfire in my 2005 chevy cavalier was caused by the coil pack going bad.
on the 2005 its a on piece design that mounts right over the valve cover. Looking at about around $100 for replacement. Of course I replaced the ignition module too which mounts to the top of the coil pack.
ignition module looks like a heat sink from a computer