I have seen lots of coil packs go bad on those cars, as well as the mass airflow sensors.

If you get misfire codes, you can access the spark plug coils by removing the coil covers along the top of the valve cover.

With the car running ,get a pair of pliers and unplug the electrical connector one at a time from each coil pack.

If the idle gets worse, you know your coil is good.

If the idle does not change, chances are you have a bad supressor end and or coil.

You may get away with just the bad supressor end, but if you do have a bad coil, replace the supressor end too.

Usually the air mass with give you multiple misfire codes.