Yaris '02 - sluggish pull away.

[Jeanne]

Every morning I start up my car and drive to end of my close, 800mts, no problem. Stop to pull out right into main road - eek its so sluggish. It only happens once - the rest of the day is fine. I have heard of something you put in the petrol tank, rev the car and it 'cleans' the petrol. Could that be it. Don't get to technical please.