Car was previously cruising and idling at 14.7 AFR.
It used to hold 14.7 on cruise quite steadily but recently its has become erratic and struggles to hold 14.7, goes leaner.
But the real issues is idle AFR. When I come to a stop it'll be 14.7 for about a second then it will creep over to 15.5 and start holding there. Then it'll jump between 15 and 16 but kind of center around 15.5.

WOT AFRs are unchanged and still remain the same as before when I had dialed the fuel trims in and the cruise and idle AFR's were behaving themselves. LTFT Low is -1.5% at the moment and LTFT Mid is -1%.

So I was thinking maybe the lean idle was a boost leak (I have yet to do a test, but seeing as WOT AFRs are unaffected does this look like an 02 sensor going out? Car is a 2001 VII with 95000k's on it, I doubt the sensor has ever been changed out.

 

This is your stock placement o2 I take it then? I would def check for boost leaks, and has the weather changed dramatically since tuned? Do you have an AEM or something similar to monitor AFRs?

 

Yes this is the stock front O2. No significant weather changes. I tune the car myself and there's no weather change that would cause such a large deviation in idle AFR only. I have an AEM wideband for monitoring AFR.

I will do a boost leak check soon but if WOT AFRs are still good and fuel trims are negative even though the car is running lean doesn't that point to a dying O2 sensor?

 

I think so..

 

Usually a dying O2 will present itself as bad mileage and very slow response to needed mixture changes.

 

Well mileage has only seemed to drop a bit. It is slow to change, like if I come to a stop it might start at 14.7 and slowly creep to 15.5. Or sometimes it starts at 15.1 and then creeps to 16.

 

Update: did some WOT pulls yesterday and was shocked to see that I ran as lean as 12.1 under full boost (22psi).
So now the lean issue has progressed to WOT as well. I'm worried cause I'm not sure what could cause this. Would a faulty O2 sensor affect WOT as well?