The issue you are experiencing with your Pajero engine where it turns off when shifting into reverse or when slowing down could potentially be due to a few common reasons:

1. **Faulty Idle Air Control Valve (IACV):** The IACV controls the idle speed of the engine. If it is faulty or dirty, it may not be functioning properly when you shift into reverse or when slowing down, causing the engine to stall.

2. **Vacuum Leak:** A vacuum leak in the intake system can disrupt the air-fuel mixture causing the engine to stall when the load on the engine changes, such as when shifting into reverse or slowing down.

3. **Dirty Throttle Body:** A dirty throttle body can disrupt the airflow into the engine, affecting its idle stability and causing stalling when changing gears or slowing down.

4. **Fuel Pump or Fuel Filter Issues:** Insufficient fuel reaching the engine due to a failing fuel pump or a clogged fuel filter can cause stalling when the engine is under load.

5. **Transmission Issues:** Problems with the transmission, such as low transmission fluid or a faulty transmission solenoid, can also cause the engine to stall when shifting into reverse.

It's important to have a qualified mechanic diagnose the specific cause of the stalling issue to ensure it gets properly repaired.