Just got an 1986 RX-7 and I'm trying to figure out the characteristics of rotaries. When fully warmed up it idles around 750-800rpm which I understand is normal. When I rev it, it falls down to around 550rpm shudders briefly and then settles back to nominal idle. Is this normal for a rotary?

I tried searching to avoid the flames, but it's kind of a specific question and I couldn't find the answer. If this is a fault is there a specific name for it? what does it indicate? I'm pretty fluent in the traditional world of pistons and I know a little about rotaries. I Just need a little time to get the feel for the strange little buggers.