AFR slowly richens at idle

Cam has 46 degrees overlap exactly. I can't run less advance, its already a comprimise from 36. As stated in my initial post, the lowest rpm drop is with 13.2-13.4 in park and 14.0-14.2 in gear. I decided to get new converter, something that will be future proof, went with dynamic 9" 4800 stall witch mechanical diode. My old converer was not nitrous ready anyway. I will update whats the situation after I get parts. Since I'm in Europe, its probably going to take some time.