Steady CEL. Runs great. Absolutely no problem accelerating. Don?t hear or feel any misfiring. There is a slight rumbling sound when I first start to drive the car, but to me, the sound doesn?t seem come from the engine, but rather underneath the car. It goes away when I continue to drive. Since winter began, I occasionally feel a very slight hesitation during idle?happened once or twice lately. Again, I only feel justified in mentioning it simply because of the codes that were generated. None of my passengers have made a comment about the idle or the drive. My friend, however, made a remark that occasionally, there is a very very very slight hesitation at the downshift when braking. No crack in gas cap. Great fuel economy. No problems accelerating at all. Never hear or an actual misfire, which I take it, means a problem when accelerating, a jerking, or popping noise.
Took it to a dealer. Codes were 0300, 301, 302, 303, 304?302 generating most often. Dealer recommended new ignition module and plug replacement, but they said it wouldn?t be a guaranteed fix and that it may need EGR replacement (don?t hear knocking though) or be a burnt valve in the cylinder, which would cost me $1500. No suction out tailpipe, no rotten egg smell (signs of burnt valve). What are the chances of burnt valve in a car with 54K anyway? Also, my maintenance schedule claims that I don?t need new spark plugs until 100K. Is there anything else this could be such as a dirty injector system, fuel filter, fuel pump, or air filter? Again, overall, the car runs GREAT! Should I just wait and see if the misfire becomes more pronounced so when I take it to a mechanic, they won?t be looking for a needle in a haystack?
Hmm, You may want to check the emissions warranty. The EPA requires these systems to function correctly for at least 80K miles. The computer cannot be putting out errors on a correctly functioning system. You might want to push the dealer a bit on this. If your state has inspection your car will not pass with these errors.
Thank you so much for your input! As we know, Saturn is no more, so I would have to go to a GM dealership and mention this? I briefly researched this warranty, and the 8yr/80K clause applies to “certain components.” Would you also happen to know where I can find out more regarding what components (areas of repair) are covered and what areas would not be covered? Again, thank you so much for pointing this out to me! Maybe some others will join in on this case! 
I doubt that there is anything here still under warranty though I wouldn’t say not to check it out.
If are no issues of warranty or recall you don’t need to take this car to a dealer. Find a reputable, local, independent shop that has people who are good with diagnosing driveability problems.
It sounds like the dealer’s shop wants to guess. This is a very expensive way of diagnosing a problem.
Someone should pull your plugs & wires & inspect them. (While the plugs are out it would be a good idea to check the compression). Ignition modules can be tested. Someone should check your fuel pressure, fuel pressure regulator, and electrical integrity of your fuel injectors and their wiring. Someone should also check for vacuum leaks.
There are three specified major emission control components,
covered for the first 8 years or 80,000 miles of vehicle use on 1995
and newer vehicles:
* Catalytic converters.
* The electronic emissions control unit or computer (ECU).
* The onboard emissions diagnostic device or computer (OBD).
Catalytic converters are critical emission control components
that have been installed on most cars and trucks manufactured since
1975. Since engines don’t burn fuel completely during the combustion
process, the exhaust contains a significant amount of harmful
pollutants such as carbon monoxide, hydrocarbons, and oxides of
nitrogen. The catalytic converter aids the conversion of these
pollutants to less harmful substances such as carbon dioxide, water
vapor, nitrogen, and oxygen before the exhaust is expelled into the
environment.
The electronic emissions control unit or computer monitors
certain powertrain functions and controls various operating parameters
to help the vehicle run efficiently and with the lowest possible
emissions. Ignition, transmission function, air injection, exhaust
gas recirculation (EGR), engine operating temperature and fuel system
parameters are some of the systems monitored and/or controlled by the
electronic emissions control unit.
The onboard emissions diagnostic device monitors the operation of
a vehicle’s emission control system and alerts the driver with a
dashboard light when malfunctions occur. The system will record where
the problem is occurring and assist automotive technicians in
diagnosing and repairing emission control malfunctions. Since some
emission control malfunctions do not have an adverse effect on vehicle
performance, they can go undetected by the driver for quite some time.
The onboard diagnostic device will help catch malfunctions early,
preventing a significant output of harmful exhaust emissions from your
vehicle, and possibly in time to be covered by the emissions control
warranty. Often this “device” is part of the electronic control unit
mentioned above.
In the future, there may be other parts or components that
qualify for this coverage. Check your owner’s manual or warranty book
for possible additional coverage.