I have been dealing with CEL problems for almost a YEAR! And I'm getting tired of it!
The car is an 06, manual.
I've read the post "Engine mis-fires? Read This First!" and most of the things on the list have been done, except actually pulling the engine, removing the heads and looking at the valves and guides. (I REALLY don't wanna go THERE)
My neighbor has a scan-tool, so we were able to pull the codes, and here is what we got:
P301 Cyl 1 misfire
P304 Cyl 4 misfire
P1153 O2 sensor range high
P0131 O2 circuit low voltage bank1 sensor 1
The car seems to drive ok, although I do notice a little stumble once in a while at idle.
The air box has been replaced because I used to use a K&N and it broke the lid tabs which freaked out the MAF sensor. And the MAF has either been cleaned or replaced, I don't remember which right now. Have also used BG Chemtool with some success. (My shop tells me to run nothing but Chevron. No cheap stuff.)
The shop I go to specializes in foreign cars, mostly BMW, Audi, and Porches, but they also service a lot of Subarus, so they have experience with the cars, but I'm thinking about taking it to a Subaru dealer shop, because they just haven't seemed to get rid of the problem for good. Despite the fact that I trust the guys at my local shop.
The cyl mis-fires appear on all cyls. That is, I have seen them show up on all cyls, just not all at once. This time, it's 1 and 4, last time it was 3.
Could there be something wrong with the O2 monitoring system that could cause the misfire issues, considering that I'm getting those error codes too?