cant find a good idle

I got another one, when the car warms up idle works it way up to about 1800 rpms then drops real quick to7 or 800 (dosnt stall) then works its way back up again and drops, does this car have an idle control sencer or just the valve? 91 crx si. any ideas would be great help

You have a vacuum leak on the manifold of one of the hoses.