P2096 CEL Post catalyst fuel trim system too lean (Bank 1)

I keep throwing this code. I hate CEL lights. I have a APS turbo back exhaust on the car and a gutted stock intake box. This CEL will pop about every three days then I clear it via negative cable removal from the battery. Its very annyoing to carry around a 10 mm wrench. I tried the Anti-fouler mechinical fix, and I went about a week with no problems, then this morning on my way to work at crusing speed, CEL... I hate this thing. I have read and read over at NASIOC, but no one has a clear answer that I have come across yet. Any clues on what to try?

INFO:
05 STI
APS Turbo back exhaust
gutted stock air box
Aproximattly 30,000 miles on engine

Sounds like the front 02 sensor might be going bad.

I'm kinda with Fuji on this... The manual Diagnostics Procedure suggests it's the rear O2 sensor related and it is post catalyst which makes sense. But as Rek suggested it could also be the intake has been modified because the procedure also makes mention of that and the MAF sensor.

Thanks for all the feedback, the gutted air box meant that I removed the snorkel and silencing material out of the fender well. Not an uncommon mod for subaru's. The MAF is still in oem placement. I do not have a cobb ap for this car . Would that help resolve this issue? I was guessing more along the lines of the rear O2 sensorhaving a problem. Thought someone else may have had to tackle this problem.

I did the snorkel removal on my GR and it led too no issues so I highly doubt that, as it does not increase air flow, only increase noise vibrations so the intake can be heard. It sound much more like the TURBO BACK exhaust is causing the problems. It is highly suggested to get the car tuned if you are going to be doing any engine modifications to the car. Also until you get the AP, or some form of tune I would suggest your drive around with the CEL flashing and the car in safe mode. The reason being, your air to Fuel ratio is way off, this may cause severe knock (detonation) which is the leading killer of the EJ257 (besides ignorance and stupidity). When in safe mode (CEL on) your car defaults to a separate map too try and keep the motor alive. Quick question for you OP, do you notice any stumbling or hesitation under partial and light throttle like daily city driving, if so it might be the front O2 sensor. Other wise I am going to say it is down to the new downpipe.

Bottem line, either get some one too tune the car if you are in an area with a large number of shops, or pick up a used Access Port from on line.

Yeah, I would also recommend a tune for your downpipe.

Thanks Vermont. There is no hesitation or stumbling, the car runs like a champ. I also believe that its the catless exhaust causing the problem. I just didn't want to "assume" anything before checking with the panel of experts.

P.S. If anyone comes across a Cobb AP for an 05' STi for a smokin price in your online travels, Keep me in mind!

PM some of the vendors, they can probably get you a pretty good deal!

***UPDATE***

So I have been driving the car for a few weeks with the mechanical fix in place and no CEL thus far. I am going to still get an cobb ap to tune for the exhaust, but this seems to be getting me through for now with no CEL's

Glad to hear everything looks to be running fine. You'll notice a hell of a difference with a proper tune!