I having a problem with idle, I set my SAFC to -8% at 1k (I have 550s and BC 272s) and it idles fine but my low fuel trim is 138 is that bad I do not fully understand the trims. Rest of the SAFC in low are around -18% and it pulls just fine. And also the only way I can stay around 15 A/F is when I put the SAFC at -8% at idle anything else and it runs to rich or to lean.

What 550s are you using? Is your ECU adjusting for deadtime of the alternate injector? Most aftermarket injectors have a longer deadtime. In non-nerd speak, there is a mechanical delay between when the ECU tells the injector to fire and when it actually begins squirting fuel. This is caused by and dictated by the design of the injectors guts becuase there are moving parts and magnetic fields that all have a time required to operate.

If the injector is to fire for 20ms to give the right amount of fuel and the injector has 300us of deadtime - the ECU must know that and fire the injector for 20ms+300us and do it 300us before it needs the fuel. That way the full 20ms of fuel are delivered right on time

If your ECU thinks the deadtime is stock and you have aftermarket injectors, the time the injector is open is actually shorter than what the ECU thinks and less fuel is delivered. This is most evident at idle. At a fuel trim of 138 you have exceeded the control limits of the ECU. It has added as much extra fuel as it can.

Quoting The_Big_Weave:
Rest of the SAFC in low are around -18% and it pulls just fine.



The AFC LOW settings are mainly going to affect closedloop operation, like idling and light cruising. As Dan said, the ECU is trying to compensate for the fact that you are removing too much fuel in closedloop. For the best drivability you want the fueltrims to be much closer to 100 if possible. What are you using to adjust the settings, a wideband? What brand are the 550's? You say that it runs too rich at idle without the AFC at -8%, but did you reset the ECU and give the fueltrims time to set first? How do you know its running rich? In closedloop the ECU usually knows better than you do as to whether its too rich or too lean, and it will fight any changes you attempt to make.

FIC 550s. I told the battery off and reset the ECU before I put them in.