3.3 newbie question: 89 engine management systems and idle AFR`s

[Simon930Berlin]

Hello,

now that I got my 3.0 TC purr like a cat with steady idle and the right AFR's I was about to help my friend with a 3.3 from 89. The idle AFR was at 19, car ran bad, chasing idle, and sometimes dying off.

Now we played around and the car seems to be working ok at 15 AFR, still chasing idle, still not perfect.

I checked under the drivers seat and there are two boxes, is there a standard 89 digital engine management system that interferes with anything I do with the idle screw?

Thanks as usual for any help,
S