Mine has done the same thing since i bought it a year ago - 06 g6 3.5l, When I start it, it turns over but then I need to give it gas or it will stall out. Once it idles it's fine. Sometimes it will do this and sometimes it wont, and once in a blue moon it will not start at all only just keep turning over until I give it a bunch of gas. (It eventually starts on the 2nd or 3rd try of turning the key and pumping gas.)
It really makes no sense to me since nowadays we have fuel injectors. and air leak would probably make sense though. I do sometimes hear an air leaking sound when the hood is opened with the car running.
Best of luck, hope you get it fixed!