Weird Idle

Good morning everyone,
I experienced a rather unusual idling issue today on my way home towing the boat from a fishing tournament.
After being on the road about an hour I had to stop to relieve myself at a gas station, I left the vehicle running with my buddy passed out inside.
Before I got 10 steps away from my truck I heard the idle fluctuate and rev from low to high 3 times. It wasn’t the normal valve timing sound but almost like someone reving the motor 3 times about a second to 2 seconds apart.
Has anyone else experienced this issue? So far I’ve put 5k miles on this truck and this is the first time hearing this.

 

Atkinson cleaning cycle I think. Mine does that

 

Could be the AC compressor requiring more juice

 

Mine does this as well... as Toyota claims "its normal"

 

I know the normal revs from compressor draw and the valve timing but this was rather unusual and caught my attention. This is my first time ever hearing it.
Honestly it sounded like an early 90’s Supra that was just starting and the idle was high and low many times before it settled back into a normal rhythm