Revs go up and down when braking

[4R_in_Uzb]

My 1990 4Runner has this thing; when I push brake pedal the revs go up and down. It doesn't happen all the time, first I thought it was heppening when the engine is cold but now I don't think it's true.
It starts to do that when I just slightly touch the brakes, even before the car starts to slow down but the stop lights light (anyting to do with wiring?...)
I was told it's probably brake vacum thing (don't know what it's called). Can anyone help me with where to look for the solution?

Thanks.

 

[TheBlueWave]

My 1990 4Runner has this thing; when I push brake pedal the revs go up and down. It doesn't happen all the time, first I thought it was heppening when the engine is cold but now I don't think it's true.
It starts to do that when I just slightly touch the brakes, even before the car starts to slow down but the stop lights light (anyting to do with wiring?...)
I was told it's probably brake vacum thing (don't know what it's called). Can anyone help me with where to look for the solution?

Thanks.

The brake vacuum thing is called the Brake Booster. It takes vacuum from the engine and converts it to brake power. I would check around for leaks in the vacuum lines and system near the booster.