Started having this issue about 2 weeks ago. Start the car and it idles at around 15 AFR, when I start driving it it becomes normal and can go into boost fine with very safe AFRs; however when the coolant temp reaches 170F +/- 5F it starts running very lean, 15.5+ and starts to spike between 13 and 17AFR! I have done nothing that could have caused this issue to pop out of nowhere and have since bought a new Walbro pump and eliminated the stock pump sealing mechanism with a clamped hose so there is absolutely no chance of a fuel leak or pump failure, I have just replaced my AFM with a used N370 unit and the problem has not been fixed.

Any leads would be helpful

Car's setup

s5 turbo swap
BNR stage 2 turbo
Rtek 2.0 ecu
HKS 750cc primary
Greddy 1000cc secondary
AEM Tru-boost
AEM water temp gauge
AEM AFR wideband O2

 

Can you track coolant temps with the Rtek, and if so, do they track normally?

 

coolant temps match the AEM gauge, let it warm to 187F just idling and the idle leans out at around 175F , I think its a temp related since its fine up until that point no matter driving or idling.

 

did u ever find the problem??

 

if you are running the emissions, with a working ACV, the air pump air is injected into the exhaust ports, and the wideband will read very lean numbers because of the extra air.

in other words on a stock car, its normal to see wildly lean numbers between idle and about 2500rpm

 

Wow, ok, forgot about this thread.

The problem was solved a while back.
I started inspecting the piping and manifolds for air leaks. I found two things that might have caused the issue since after they were fixed, the problem disappeared.

The car's emissions have been completely removed. I checked the intake pipe after the AFM, its just a solid aluminum piece. I checked the couplers and one of the clamps seemed loose. I ended up getting a better fitting pipe and T-bolt clamps. drove the car and it seemed great. My guess is the air leak between AFM and turbo caused the turbo to suck in more air than the AFM accounted for.