2003 Buick Lesabre will not idol in mornings

In the mornings, the car will start fine but will not idol or even run at first. I press the the gas pedal and it just dies. However, after restarting and finding the right spot using the gas pedal, I am able to keep it running but still will not idol unless it is in park and even then it is rough. Usually after the car has been running for a half hour, it will automatically start running fine as if someone flipped a switch and then will continue to run fine for the rest of the day....even if the car has been shut off for a few hours. However, the next morning it all starts over again.
So far I have cleaned the mass air sensor and replaced the air filter and fuel filter. My spark plugs have never been changed which is my next move but I'm not sure that would cause my symtoms.

Please advise...

Darren