very short trip makes car (wrx) unstartable?

You probably loaded the engine up with fuel by starting it cold and running it for only a few seconds. On cold starts, especially in colder weather, the fuel mixture is very rich to help the engine start and run until it's warm enough to properly atomize the fuel. If you shut it down immediately after startup, the extra fuel will remain in the cylinders and foul the plugs making the next startup difficult. For the future, try to avoid running the engine for such a short time. Also be aware that there is a "clear flood" mode which works by holding the pedal down to the floor (but not pumping) as you crank the engine. This tells the ECU to shut off the injectors so no more fuel is pumped into the engine and the flooding can be cleared. Once the engine starts release the pedal. This procedure is explained in your owners manual.

cool! i thought that trick only worked on carbureted engines - i guess it made sense to carry it forward to the "brave new world" of electronic fuel injection...

The clear flood procedure is indeed mentioned in the manual, but it still feels counter intuitive..

Thanks. I will never run the car for a few seconds again.

I know, but it is pretty much an industry standard. I think it is a hold-over from the carbureted days when we would do the same to clear a "flood." Holding the pedal down opened the choke, so the mixture would be leaner. Weird, huh?

Mike

On carbureted engines, this works by forcing the choke slightly open thus leaning out the mixture. On modern fuel-injected engines, the ECU is programmed with a special mode that will shut off fuel to the injectors if the pedal is floored during cranking. So, same driver action, same result, different reason.