Why does my car die when I am idle at a stop light?

OMG I have the same problem. I went to get it checked out and the mechanic said he found nothing wrong with it. So all he did was like clean the engine and stuff. So yesterday i'm getting ready to make a right on a red i check traffic to see if it was clear for me to go and right when i put my foot on the gas my car shut off. I had to put it in park and then start it again and go. I'm so pissed that it is happening, So what i have been doing is know when i'm at a red light i put my car in nutreal (sp?) so then when the light turns green i just put it in drive and go.