Check that the accelerator cable is moving freely. If not replace it with a new one.
If you are using supermarket petrol, switch to decent stuff. The Corsa I had would not run properly on supermarket petrol. I switched to Texaco, Shell, BP, Total or Esso and the problem disappeared after a couple of tankfulls.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.