I have a 1999 Saturn SL2. It is throwing code P0302. I had it read and assumed the same thing, plugs or wires. I just replaced them both. Good high quality stuff not the basic cheap stuff. I still had the misfire. During a mechanic friends inspection ( very basic ) he arced the plugs off the block to ensure they are all firing. They were. He cleared the code. It threw again. I decide to check the fuel injection since that was in the code as well. It seems that the noid light would not light on the far right cylinder, don't think that is #2 but that is the one it did not light up on. So I have no idea what to do next. I doubt a car with only 137k miles on it needs a new computer but I don't know what to do to see. Nor do I really even know where the computer is, another forum here someone commented that a pin just got loose on the ecm he put it back and all was well. I dont even know where the ECM is so I dunno how to do that.

 

Check your connector and the wiring on that particular injector. Far right cylinder when you're standing in front of the car looking at it? If so, that's #4. If from behind the car, then that's #1.

 

A P0302 means that the computer is detecting a different voltage level when firing or attempting to fire the #2 spark plug. Most often that is the spark plug that has misfired, resulting a higher voltage at the coil. A very low voltage due to an arcing wire is the second most common culprit.

It can happen with an incorrect fuel/air ratio or compression issue as these affect the voltage required to make a spark at the tip. I assume you replaced all your plugs and wires as mixing old and new can cause a misfire code. At this point, I'd be looking at the 2/3 coil itself. You might have a crack around the #2 tower or an internal winding issue. You can simply swap the two coils and see if the issue moves.

You could also just swap the wires. If the code changes to a P0303, then the issue is something in the #2 cylinder, if it stays the same, then its the coil. You will need three drive cycles to see if the codes switch, in two drive cycles, you will get a 303 and a 302 if the issue switched, it just hasn't cleared the 302 yet. In one drive cycle, you should get a pending 303 if the problem switched.