Nissan Repair: 88 pulsar q, vacuum booster, air control valve

Question
i have a problem with my pulsar and i don't know where to start looking for the answer during the day when i put my foot on the brake the engine revs drop to about 700 when i take my foot off it comes back up when i do it at night with the headlights on it stalls the car. i thought at first it might be a vacuum problem because when i pump the clutch it seemed to go fine for a while but then i realized it was worse when the lights are on so i am wondering where do you think i should start looking for the problem

Answer
Mia,

Sounds like the vacuum booster is blown and the brake actuation causes the vacuum to bleed off and open up a source for a leak, blown diaphram, and that causes the drop in RPMs.  The headlights get enough of a load that it kills the car when the brake is depressed.  I would check the vacuum booster first, the check valve, on the hose and the idle air control valve.