ok my Merc Marq 4.6 when you start it sometimes in the am it will start and just quit after a few minutes, why ??

 

Any other symptoms? Like rough idling. Probably the Idle Air Control valve. It's worth about $70 from the parts depot at Ford and an easy install. You could try cleaning it but I didn't have much success with cleaning.

 

i too vote iac, idle problems that stall are typically the IAC or vacuum leaks. I cleaned mine which helped. Take it off, wd 40 first, then carb cleaner. Put it back on. Clean the MAF too while your in there and check your vacuum tubes, esp the one from the passenger valve cover to the rear of the TB, those like to break and crumble.