1999 Pontiac Sunfire Engine rough idle issue.?

Change the spark plugs and the spark plug cables. After that, get some fuel injector cleaner and throw it in you gas tank. If it persists, then you need to change your coil packs. before you d so, remove the spark plugs one at the time for your coil pack, and check to see if the end bits are rusty or dirty, if they are, the either clean them if dirty, or replace them if rusted. If all this it still persists, then shoot me an e-mail and I will trouble shoot it with you. I just got done with my wife's 99 sunfire. They are really to easy to work on. Whatever you do, do not go to a garage, they will charge an arm and a leg for the 5 minutes of work. Like I said, if after all this it still gives you issues shoot me an e-mail and I will walk you through it by e-mail. I do everything on my wife's on myself. J body vehicles like sunfire, are the easiest do it yourself cars in the world.

Jordan

This is not a sensor issue because it would affect all cylinders. 99% you are dealing with a bad fuel injector. The easiest way to make sure is to measure resistance of all injectors, and see if the first one is out of line. If I'm not mistaken, the injector for this engine should be in the range 1.9-2.1 Ohms. One note: unlike other gm engines, this one did not have a typical injector problem. Somebody already mentioned the coil pack - that could be the problem as well, it's just easier to start checking with injector.

The ignition system fires the spark plug in pairs, so if you put a new spark plug in and it did not fix it it's probably not ignition related. Most likely your #1 fuel injector is bad or plugged up.