We've seen maybe 15 STi's that run fine 99% of the time, then randomly throw single-cylinder misfire codes and idle poorly. We usually end up replacing the injector in that cylinder under warranty. There were a number of cars that did this, and replacing the injector was all that worked.

SS

 

I should probably clear the code and constantly monitor for error codes. Good idea? Or should I just bring it in...

 

I would take it in, warranty is something to take advantage of..

 

I threw the same code, but it was because I was testing my methanol and it made the engine stumble, but the accessport would not read it either. I was having misfires in cylinders 3 and 4 and all the accessport would say was "12" and "31" where it should have had p0303 and p0304.

 

My accessport doesn't read any error codes at all!? not even a 12 or 31. I do notice that the idle is slightly rough at times, I always thought it was just the way the STi is... Is it supposed to be perfectly smooth at idle? Could bad gas cause any of these problems?

 

Are you just Cobb Stage 2? Have you been protuned? What are your mods? I had a similar problem when I was running Perrin modified injectors. If you are running larger injectors, it is a good idea to have the idle turned up closer to around 800-900 rpms. I have been told by Jarrad of PDXtuning, that Cobb has had problem with some of the code writing when it comes to misfire codes. When my car was misfiring, I had Jarrad turn the misfire codes off, but I would still through a CEL. Then at that time, my AP would not recognize the code that had thrown the CEL, but it would clear it.