I have a 2002 WRX with 162,000 on it. I bought it a few weeks ago and I just started having some issues with it. On my way to work last Friday, the car started to bog down and then my CEL started flashing. I pulled over and shut the car off. From previous experience on another car, i knew the car was mis-firing. I let the car cool down a bit, and then started it back up. The code was gone, so I decided to drive the car back to my house. about half way back, again the CEL started flashing when I was at low RPM. If I downshifted and kept the rpm's above about 3k, the CEL stayed on, but did not flash. I got the car home and parked it.
Using another car, I got a ODBII reader and read the codes. I had mis-fires in all 4 cylinders. I reset the ECU by disconnecting the battery and holding the brake petal down for awhile. When I started the car up again, it ran fine for a few minutes, then the CEL started flashing again. I read the codes again and was just getting P0304 (mis-fire on cyl 4). I repeated this a number of times to try and get other cylinders to mis-fire, but could only get cyl 4 to give me a code.
Yesterday I replaced the spark plugs with new NGK-G-Power plugs (#7092) gapped at .030. Same P0304 code.
I then switched the coil packs from cyl 2 and 4, and still P0304 code.
At this point i'm not sure what I should do next. I was thinking about doing a compression test to see what the results were. If that turns out ok, I think it might be a bad injector? I took a look at how to replace the injectors because I thought i might just switch the cly 2 and 4 injectors to see if the problem followed, but doing that is a ton of work.
Let me know what you all think. Thanks for the help!