Idle surgs when brake pedal is pressed.

My friends 1988 22re pickup is surging when you press the brake pedal. I know this isn’t a Tacoma but does anyone have any advice on what’s going on? Is it the brake booster, master cylinder, or both? Here is a video of what’s going on.

When I plug the vacuum line going to the brake booster the idle surges, but when I unplug it the engine runs rough but stops the idle surging.

https://youtu.be/0RcXOHAfh44

 

Could there be a blockage in the booster to cause this?

 

Never mind it was the timing and the idle. Sorry for the extra post.

 

At least you figured it out

 

there still could be a bad booster. With the motor off how many brake pedal applications do you get before the pedal get hard. 1 to 2 applications is normal. If the pedal is rock hard immediatly after the motor is off either the check valve, if it has one, is bad or the booster has a crack in it.