Help! Engine starts but cuts out after a second

I pulled into a gas station to install my new license plate. Initially started car, sounded quick and fine until the engine died like a second later. The engine is smooth so the only way I could tell was lack of sound an the tachometer. Tried it again and did the same thing! The third time I started it and gave it a little gas for a minute or so and went on my way. The engine should have been warm before I pulled off because I had been driving for a few miles to pick up some parts...
...what's the deal? Am taking it to be looked at Friday at Duff's subaru anyway, it would be a good time to ask there too. Suggestions??