Hello all, first post in this sub-forum because despite the fact that I’m a pretty experienced tech, I can’t quite get to the bottom of this. Maybe I’m overthinking it because it’s my own car and some outside feedback would be much appreciated.

I know a lean idle would immediately indicate a vacuum leak and yes I’ve smoke tested. No leaks on B1.

My car:
F21’s, recent timing belt, 10w40 Amsoil, srm intercoolers, XS power exhaust (catless), XS tubular exhaust manifolds, Bosch 630 ev14’s, stock maf and fuel pump. GET tuning on a conservative boost tune with some timing.

My Issue:
My B1 wideband is reading anywhere from 18-22 Idle/cruising with occasional dips in the 14s. Started about a week ago.
I swapped my wideband from b1 to b2 and b2 idles perfectly between 14.5 and 15.3.
WOT pulls my B1 AFR is between 11.8-12.5. So MAF seems ok as well as fuel pump as it’s keeping up.
Smoke tested today. B2 has a small vacuum leak at the cam chain tensioner, but it is not throwing a code/affecting performance. B1 has absolutely no leaks, boost or vacuum. Spark plugs are new and properly gapped.

The codes I have
P1476- EVAP leak detection pump malfunction (blew apart, not sure how). I capped off the line running to it and the purge solenoid as well. At this point I don’t think it’s part of the equation. As my car ran fine previously.
P0103- MAF signal too high. Stock maf pushing 19lbs on F21’s. Only sets after WOT pulls and reads about 5g/s at idle.

P0130 (I’ve been reviewing this code for a couple months now)- b1s1 circuit malfunction. 02’s were new as of last year and part of my refresh. I replaced both bank sensor 1’s 3 weeks ago preventively; thinking I used a cheap quality sensor (2 eBay yellow box Bosch sensors with Chinese writing). Replaced with blue box Bosch sensors from FCP. P0130 remains.

Both sensors are switching at the same time when I view mV. Doesn’t appear that the B1 sensor 1 is getting stuck lean or rich, which according to the Audi code book would trigger this.
The secondary requirement for this code is the s2 on the same bank not switching within 90 seconds.
My rear 02’s are coded out, but my wideband is tapped into the B1S2 voltage feed for tuning purposes. I’m thinking maybe the voltage from the wideband is throwing this code?

My thoughts currently are either an exhaust leak that I’m not hearing between the primary 02 and the wideband, or a timing issue.
I say timing issue because last night, my car was running perfect AFR at idle. I had my scanner with me (it’s attached like life support) and noticed fuel trims were fine, but my B1 cam angle was switching significantly more than the B2 cam angle. No codes thrown for timing though, so I’m certainly a bit lost here. (Trying to diag a healthy car, HA!)

TL;DR: B1 wideband specifically is lean. No boost/vacuum leaks. P0130 B1S1 O2 code doesn’t seem related.



I can post logs later tonight if necessary, but as my issue is idle/cruising and not WOT, I’m not sure how much they’ll help. But you guys know more than me. Any feedback is greatly appreciated.


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