Misfire in 3rd Cylinder

Check your coil(s), do a compression test, don't just guess. Start by changing plugs, from 1 cylinder to the next, spark plugs can misfre and be brand new, I have seen lots of guys assume it was this or that and all along it was a basic component. If you have an injector out you should have a P02XX type of code, do you ? Also does your Subaru run hot or use coolant? We do about 1 head gasket job on a 2.5 Subaru per month in my shop. When was the last time had you valves adjusted, check this because many 2.5s have adjustable valves and when they get tight they set misfire codes like crazy. here is a link to a web site with wiring info: http://bit.ly/mitchell_repair_manuals_online

If you have recently replaced a timing belt than consider that the left side cams may be off 1 or 2 notches. This will cause the symptom you described because the camshaft sensor will read this and try to compensate. HENCE: Rough idle and CEL on or flashing because ECM cannot pull it far enough into range, so it will pick middle of the road and stay there. I have been burned on this before and will not forget it anytime soon.