Brand New Mazda Protege5 stalls !

I have a brand new Mazda Protege 5 Automatic (Bought it 6 months ago).
At red lights or stop signs, the car stalls occasionally.

This is an intermittent problem, and only happens maybe once or twice a week
.... usually on humid days.

Dealer is useless, they cannot pinpoint the problem ,and their computers
read "no problems".

Has anyone experienced similar problems, or have any suggestions.?

Any feedback would be greatly appreciated.

Many thanks,

Steve.