I play vanilla and I have two married couples who have woohoo'd autonomously. It was years ago, though.They woohoo'd many times autonomously during a short time period. I remember reading about it on the forum, it was common then, it was probably added on some patch. Then it suddenly stopped and I heard that they'd disabled it because so many people complained about it.
I'm not 100% sure if it happened like that, but one of my couples were like rabbits when they were both on a flirty mood back then.
Some time ago one couple made out in the closet autonomously. but I haven't had any autonomous woohoo in my game for a long time. I wish it would still happen.