Do you have an aftermarket intake? If you had a similar breakage to me, it would cause the problem all the time, plus you would propbaly get thrown into limp mode (1.2 corsa power). You could have a faulty, but not broken N75? I dont have any pictures of the pipe sorry, but unless you've had some work done (eg:timing belt) it is unlikely you have a breakage. Perhaps look at plugs or other ignition components? Scanned for codes?