Running Rich at Idle, Lean while crusing or under boost

[S13srdave]

I have a redtop sr that runs rich (11:1-13:1) at idle, then leans out severely (16.5:1-18:1) while just cruising or under boost (13.5:1-15:1).
Mods:
-2871r. 64ar
-MSD 72# injectors
-Z32 maf
-Walbro 255 FP
-currently only running 7psi until i fix this fuel problem
-NGK coppers gapped to .027
-Timing is set to 15* BTDC
- compression is a little low, about 130, but is the same in each cylinder

I've had this problem since rebuilding the motor. I just got my JWT ecu back and installed last week. At first it was running lean all the time. Pulled the codes off the ecu and was getting a code 11 and 12. Wind up replacing my maf and that helped, smoothed the idle out but was still running lean. I replaced my BOV today and test drove it and found it was running richer, well turns out its only at idle. At idle, I'm sitting at about 17psi of vac and between 11:1-13:1 afr. When I start cruising, it leans out to 16.5:1-18:1 and i'm afraid to even get on it at all bc it's running so lean. Boost leaks would cause it to run rich under boost so I'm wondering what else could cause this problem. I was getting a code 11 from my ecu, and that's for my CAS. But if it was bad, the car wouldn't run, would it? Any ideas or suggestions would be greatly appreciated!! Thanks!

[onr240sxse]

I recently has the same problems as you. Mine turned out to be the spark plugs. I read that if there is too much unspent fuel entering the exhaust that it can cause the wideband to "malfunction" and read lean. Pull the plugs and see what they look like to make sure you are running lean. If not check the fuel filter and the sock on the fuel pump as well.