For those of you that have done your own tuning, did you have to lean it out considerably in closed loop at idle and low load? I'm trying to figure out if I have an issue, or just need to address this in my tune.

I'm still running largely the factory ROM, only thing I've done so far is remove the irrelevant CELs. Nothing too far from stock, my MAF tube is the Cobb one which is same diameter as factory. The only major difference from the donor car I can think of is the very short and open exhaust.

On open loop it feels fine, but idling and low load it's crazy rich, you can tell by the smell and black soot. Hesitating and minor stumbling too. The narrowband agrees, my long term fuel trims are pegged at 25% lean, and it's throwing a "Too Rich" code. I believe 25% is as far as it'll go.

Tried two MAFs, one verified working on a WRX. Haven't tried swapping the front O2 sensor but since it's acknowledging it's rich and pulling all the fuel it can and still throwing the code, I don't think it's that.