RB20DET lean on cold start

[MidnightR32]

I'm running a Haltech Platinum Pro with the stock map for the RB20DET + tweaks for my build. When I started it this morning, the IAT was at 32F/0C (Outside temp was ~42F) and the AFRs went off the scale for my AEM gauge. I let it run for ~30 seconds then turned it off. I then did a smoke test, by hooking into a vacuum line directly behind the throttle body, and confirmed there was no leaks ( i let the smoke tester run for ~5 minutes / confirmed it was generating smoke before hand ). I then started the car again, after fixing a power steering leak.... and it seemed to be happy for ~30 seconds (was at ~11/12), but then seemingly shot back up to ~18 again. I then let the car run for a few minutes, thinking this was just cold start related, but the AFRs never came back down. I didn't let the car fully warm up, so maybe this makes sense, but I'm not sure what to do?

The AFRs, when I last ran it, were normal, but because of personal reasons I haven't been able to break in the car. It was rebuilt last year.

 Engine / Mod list:

    Supertec pistons

    Spool rods

    Kelford 270 cams and Springs

    Stock crank

    Deatschwerks 900cc injectors

    Walbro 255 (Wired directly to the battery relocated in the trunk)

    NKG Audi R8 Coil packs + Conversion Harnesses from Wiring Specialties

    Holset HY35 turbo

    Haltech Platinum Pro ECU

    Haltech boost controller (wired in for high boost

    RB25 Neo transmission + needed bits for the speedo to work

 

[MidnightR32]

I've uploaded logs / the current map to Gdrive if anyone has any ideas. https://drive.google.com/drive/folders/1FPnr22Z-EilG7tYdHSi0Qb07P2jfFLKV?usp=sharing

[GTSBoy]

Put a pressure gauge on the fuel rail.

[MidnightR32]

I have one and it was at ~43.5PSI.

[GTSBoy]

I shall assume that was primed, not running.

Now it is time to suspect the wideband sensor.

[Duncan]

I agree, most likely a sensor issue. You didn't mention how it was running but above about 20:1 it won't run anyway

[MidnightR32]

Unless my sensor just died, was only a couple months old, I strongly believe it didn't. How can I test it? I never mentioned it being 20:1+?

[MidnightR32]

Oh, my misunderstand.

When the car was running, it sounded ok, but if I gave it any gas it wanted to die but caught itself afterwards. It's very different from how it was a couple months ago when it was warmer outside. The logs show that the AFRs are better during, what I assume, is warmup enrichment. Because it's cold, and air is more dense, should I work on the enrichment bit?