Originally Posted by
CaudleDynamicsLLC
Im guessing you may have meant that you can get it to idle at your desired fuel mixture in OPEN loop, but then the fuel trims bring it back rich in CLOSED loop?
What are your narrowband O2 sensors reporting at CL idle when your WB says rich - are they agreeing with your WB and saying rich as well, or are they indicating stoich mixture? (which they should if theyre driving fuel trims that direction). Is the voltage swing of the sensors relatively quick and consistent?
The camshaft overlap (EGR effect) may be throwing off the perceived fuel mixture at idle, and the long tube headers may be fooling with the transient time from combustion to reaching the sensors. Maybe poke around those two potential phenomena