So here were my symptoms. The car was running really rough and shaking sometimes due to misfires. The P0300 Engine Misfire Detected was the only code I got so I wasn't quite sure what to do. I tested the coils by swapping them one at a time with a new one, but the old ones were OK. I pulled and replaced the spark plugs, but that didn't fix my problem. I misted the plug wires with water in the dark and didn't see any sparks so I measured the resistance of those. All of them were below 10k ohms so they should have been OK, but I replaced them anyway. However, I still had the same problem. So I called my mechanic and he suggested that I might have a clogged fuel injector. To verify that they are working, pull the beauty cover, start the engine and hold the tip of a flathead screwdriver flush against the body of each injector. For the novices, the injectors are the 8 things sticking up inside the V of the engine that have a 2-wire electrical connector sticking straight up out of them. Then put your ear against the end of handle of the screwdriver while plugging your other ear. If the injector is working properly, you'll easily be able to hear a regular click, click, click. I know it sounds weird, but give it a shot. If you don't hear clicking, then you found the injector that is bad and may be plugged. Next, take a small hammer or some other object (I used the 6" extension from my socket set) and tap the side of the bad injector a couple times. In my case, that cleared the clog and the car is back to running good again. Next, go get yourself a cold one and enjoy the fact that you fixed your car without getting dirty or busting any knuckles or spending a nickel. Actually buying some injector cleaner might be a good idea even though its hard to tell if that stuff does anything.