Slight rpm bounce in warm start

[Gkazofon]

So, this happens only when the engine is warmed up. When I shut off the car to go shopping for example, the rpm follow this route

1. cranking to 1500 or so
2. drop to 750 (normal idle) for 2 seconds
3. drop to 600 or so for 1 second
4. go back to 750 and stays there

No more bounces or anything, until I shut the car off again being warm and the same thing happens again. Is it something serious, or can it lead to a serious failure? The engine is a bone stock B16A2. Thanks a lot in advance!