RPM decrease with braking

[Yukon40]

I have a 1978 FJ40 with a 2f, and I can't seem to get the RPM at idle to stay consistent. I also notice a severe decrease in RPMs under breaking, followed by an increase after braking has stopped. Could this be a bad fuel pump? Ignition? Your thoughts are appreciated.

 

[dfmorse]

Vacuum leak off of the brake booster; big red hose - maybe. And welcome.

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[Yukon40]

Thanks, I think you might be on to something.