First things first:

1. Clean out air filter, if its really dirty, replace it.
2. Figure on replacing spark plugs.
3. Change fuel filter if not done already.
4. I would inspect the idle air control valve. -read below-

With the engine warm, (when the problem is there) Remove the entire air filter assembly and have someone crank while you are depressing the air metering plate. You probably will only deflect it 1/4 inch or so. Too much, will cause no start. What you are doing is allowing more air to come in to the mix.

Edit: also try pulling up a bit.

If the car will stay started, or you at least notice some positive difference, then I would suspect that the idle control valve is stuck. It is a little cylinder looking thing towards the front of the car, about 5 inches away from the metering plate. It will have a plug, and two black rubber hoses connected.

Let me know what happens

__________________
Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2