Why won't my '92 Landcruiser restart?

If I've been driving for a little while, or even if I'm just sitting in park with the engine on, and then I turn the engine off, the car often will not restart immediately. After waiting for 10-20 minutes it starts back up just fine. Yesterday I was backing out of a parkin, it felt like the engine was chugging just a bit, and then it stalled out and would not restart. Are these things related and WHAT'S WRONG?