1996 Toyota 4Runner Engine turns off

Hello, this occurance happens at least 3 times thru out the day: When I turn the car key, engine turns on, but shortly right after it turns off. There are times that when I crank the key and give it gas so the car remains on, but once I release the gas pedal the RPMs start dropping until it turns off. After 3 to 4 tries, eventually the car will start up normal and stay on. Also related to the above, there have been times when I start the car, giving some gas and hear a popping sound from the engine. Please help me clear up my doubts and thank you.