Good news....and bad.
The good news is your are not the only one.
The bad news is that it happens to hundreds of poor hapless Vauxhall owners from Astras to Caviliers, at traffic lights and roundabouts.
It's probably a faulty idle control valve and will only get worse.
Best thing to do is get it fixed at a Vauxhall dealer than sell the car and buy a Jananese car. Go for a Honda. Put your time with Vauxhall down to experience. They are such cr*p cars. I know because I have one and it is forever stalling. The only thing sporty about it is its daft name. Astra 'Sport'. God I hate it.
Brian, August 2005