I don't see any problem using the 02 stock location.

Whether it'll be a rich / lean - that I don't know.

I've had no problem w/ my setup (other than boost cut becuase of the DP).

As for Helix w/ no cat:
Why not give it a try and see if you are getting a CEL.
Then if you do, take it to Autozone for free reading.
If it's an 02 sensor problem then you can try this mechanical fix.
(For sure you will get a CEL)

Another thing to point out w/ this fix:
Occassionally (Very rarely), I got a CEL when the weather changes dramatically or when it downpour rains out there.

Then what I did was just reseting the ECU and I'm good for about 5-7K miles or till the next weather change.

 

Anyone experiencing loss of power with this fix?

 

I don't mean to sound like a noob (well I am), but where is the O2 sensor on a 2005 STI? I looked under the car and near the middle on the DP, I see a wire with a sensor going in. Is that the O2 sensor? If so, how can the mechanical CEL fix work by extending the sensor? There's no room for the extension to fit! Let me know.

Thanks.

 

Yes, thats it. You get more space with an aftermarket DP.