it sounds like this is the dbw throttle body (but it would cause a check engine light), without the light it could be the fuel pump relay, or fuel pump signal. i would check your fuel pressures, both while driving and again when it happens.

Being it does not have all the time, happens more when its cold, and i had a similar problem (one time) it could also be the o2, or maf. but those should also signal a light.