Why might an Opel Corsa stall when idling?

You may need dealer assistance, if this is a stepper motor acting up and allowing the engine speed to fall too low.Suggest check the air filter is not blocked,you may have picked up rubbish.If ok check around the air filter for pipes adrift and around the injection unit for the same.Is the "engine electronics"warning lamp on? There may be a sensor fault or an e.g.r. valve fault upsetting the idle mixture.

i suggest cleaning the idle air control valve i had the same problem idling around 400 and cutting out on cold starts the icv is located next the the rev cable and a carb cleaner is recommended i also cleaned the throttle box and air pipes at the same time lucky for me no more idle problems previous owner over filled oil at sum point and it had got all ova the engine compartment