2005 Mitsubishi Outlander vapor pressure?

After putting gas into the car(amount not applicable) and restarting it, fails to keep the idle, dies and I need to restart(turn the ignition key) and it'll turn over but die as soon as I try drive it (put it under load). Usually on the third try I can feather the gas pedal enough to get it running down the highway. The only time I didn't run into the problem, was a cold night and she starting and ran as expected. Could it have something to do with removing the gas cap and releasing the pressure in the tank, then having to build it up again?
Thanks for your attention,
Jim Walsh, St. Martins, N.B.