Stalling car

[wadevries]

My Mom drives a four door Saturn sedan. Every once in awhile she will drive it somewhere, shut the car off, run her errands, come back, get into the car only to have it not start. She’ll call my Dad to come pick her up, but 15-20 minutes later, the car will start again. My Dad has had a new distributor cap, plugs, spark plugs,a new ignition installed. yet it keeps going it. It doens’t do it all the time and there isn’t anything that we have narrowed down to be the root cause, obviously.