The FE 90 is a macro lens. AF is not really its forte. It's very slow to focus, even when it does focus. It's really meant to be focused manually more than anything else, for up-close macro photography.
I have both the FE 90 and the FE 85/1.8. The FE 85 is definitely the one to go for if you're looking for good AF and general purpose shooting (portraits, etc).
It doesn't have a very good MFD, so it cannot be used for macro work. As long as you're not into macro, I'd sell the FE 90 and get an FE 85/1.8.
I get that but the FE 90 won’t lock focus with anything at any distance if the light is low. During daylight and outside it’s acrually quite quick. I bought the 90 specifically for newborn photos of my baby and to get into product type shots but had hoped I could could also utilise the af at times.