2004 Hard start when warm

I've got a 2004 Grand Prix with 110,000 miles and it's had a warm start issue since about 50,000 miles. (this is an electric throttle control)
It will always start when it's cold, but after it warms up it doesn't want to start very well, but if you take your foot and hold the throttle pedal about 1/4 to 3/8 of an inch down it starts up fine, runs great other than that, and pulled down 30.5 mpg on a 2000 mile trip last summer.
Any Ideas?

Check the fuel pressure regulator, and also similar threads at the bottom of yours.

clean the throttle body very well. Not many issues with the rugulator on the 04 up grand prixs. Once you clean the throttle body you should be good to go

Since it would start fine when I depressed the throttle pedal slightly I was thinking that it might have something to do with that, so while looking at the parts pictures of the electric throttle on the Napa site I saw this screw that looked to me like it could be some kind of adjustment, so I took my pedal out (2 bolts and the electric connector) and sure enough, that small screw is an eccentric. It was turned down to the bottom so I turned it to the top to see what it would do and re-installed it.
It started out idling at 1200 rpm, but after about a mile of driving it's back to idling normally, and then I drove it around all day here in 104 degree Kansas weather and it started every time, so I think I might be onto something.

I'll check the fuel pressure and clean the throttle body because it might help out some more, but I'll keep everyone posted on how it's doing.
If these pictures come through it shows the screw.

pay attention to your gas mileage. you may have just covered up the problem by adjusting the screw. Definately clean out the throttle body very well, get behind the plate. I use a really soft baby toothbrush to get the tougher stuff. I also use the seafoam penetrating spray and lube to clean it. I've noticed that it does keep it cleaner longer.

I finally stopped working on my street rod long enough to take the throttle body off the Grand Prix and clean it, and you're right it seems to have been the problem, before it use to run rough for a few seconds (if it would stay running at all); now so far it starts very smooth after cranking over and (the best part) it stays running!!!!
The throttle pedal that I adjusted earlier seemed to helped for about 2 weeks, and then it was back to hard start again, so the computer must have readjusted the new throttle pedal setting as I drove.