What would cause the motor to stop running when brakes applied for a 1997 Mercury Villager?

In a 1997 Mercury Villager, the motor may stop running when the brakes are applied due to a vacuum leak in the brake booster or a faulty brake booster itself. This can lead to a loss of vacuum pressure, which is essential for maintaining the engine's idle when the brakes are engaged. Additionally, issues with the idle air control valve or electrical problems related to the vehicle's braking system could also cause the engine to stall. Checking these components can help diagnose the issue.