u/Turt1e_was_taken

I’ve noticed this with most Toyotas I’ve had, that when idling when engine is warm, the revs sit at around 700rpm for about 15 seconds then increases to around 950rpm for about 5 seconds, and repeats.
I doubt anything is wrong since as I said, every Toyota I’ve had does this, but I’m curious to know why.
If anyone has any answers that’ll be great :)