Where is that sensor, and how could I check it?

 

Did you try cleaning the MAF with MAF cleaner? What does your fuel pressure look like when this lean condition is occurring?

 

fuel pressure doesn't budge; it's around 42.5. I do have the JWT hack of boost controlled fuel pressure increase, so it increases just fine under boost, but holds rock steady on idle, or not in boost.

I'll clean the MAF today, just in case.

 

Have you confirmed no intake or upstream exhaust leaks?

 

No intake leaks; I still need to get to the bolts on the turbos to tighten those. I was not able to do so this weekend. I'm not saying they are loose, I just don't know right now, and I can't really get under my car right now. Have to wait until the weekend.

On another note, MAF is nice and clean, and no change. Oh well.

 

Std fuel pressure is 51-52 psi. Don't know much about that, though.

 

Ok, so it turns out it also started throwing P1271. Due to this, I suspected a bad O2 sensor, passenger side, pre cat. So I just got done changing it out, problem fixed. PITA to do, though.

While I was down there, checked all the bolts on the turbos, they were all tight.

Problem fixed. Diagnosis: bad O2 sensor.