12.5 in boost is pretty damn lean especially for a ka. I always had my cars drop to 11.0-11.5 under load. A de-accel lean condition is normal though. If your foot is planted and you are pulling high 12's for afr something is definitely wrong. Try re-calibrating your sensor. If that doesn't work bring it in to a dyno and do a few baseline pulls to get an idea of what the car is doing.