Volvo Repair: engine shakes and almost stalls when car stops, volvo 240 wagon, just brakes

Question
hi
We just purchased used 1987 volvo 240 wagon- as is-!
I was told breaks were poor and I found exhaust to be in bad
shape. We drove it from PA to NY about 130 miles - it went OK -
loud but engine pulled strong up the hill. At the end of our
journey we were in bumper to bumper traffic and engine started
shaking strongly and rough as car was coming to a  stop, later
when coming to stop engine almost stalled (brakes became stiff
- didn't work) and needed to add gas to keep running - very
dangerous! I am taking a car to a mechanic on Monday -
What is your opinion on what is wrong - just brakes or much
more? It is B230F engine
Thank you
Debby

Answer
For the power brakes to work, the engine needs to be running and producing vacuum to the brake booster (big silver thing behind master cylinder). when the engine begins to stall or run rough, there is not enough vacuum to the booster and the pedal will feel very stiff. Find out what's causing the stalling and afterwards check the brakes...it's a safety item of course.