overrun

during overrun area it is shown in the graph the rpm starting from 5500 until 8000 RPM but how it can reach these numbers if the fuel injectors or the throttle is completely closed ?

I don't know the specific problem you have, but it is dropping from high to low rpm, but the way graphs are set up, it just looks like it's increasing.

Hopefully Gord's suggestion has you covered, but please let us know.

The engine would be revved up under power then allowed to pass through that area on overrun.