One thing for sure is that if you do Not repair it soon, it Can cause the computer to go bad as the excess electricity has to go somewhere. A misfire can be a spark plug, a plug boot, a coil or even a vacuum leak. Take it to a repair shop and have it properly diagnosed.
You should repair it as soon as possible because it can cause the catalytic converter or oxygen sensors to go bad. Then you are spending money you could have saved.
To the right side of the master cylinder on the firewall should be a plate with all the information you need.
A 2003 Impala does not have a timing belt. It has a chain.
Should be on the driver's side against the firewall
1800 or so
For BEST performance you should exactly what came in it and that is AC Delco.
Check your oxygen sensor.
Look on the drivers door post and there is a decal telling what the pressure should be.
It is cheaper to replace it. Finding someone to repair it is almost impossible.
Turn the key off and on for three times and that should prime the system.
It should be under the hood of the vehicle or in your owners manual.
A cylinder misfire is condition where one or more of the cylinders is not burning the fuel at the proper time it should. It can be caused by a defective spark plug or plug wire. It can also be caused by a defective fuel injector, blown head gasket, or in rare cases a burnt valve.