My 2012 Holden Captiva has low engine power and an air-leak sound

You haven’t told me which engine is fitted to your car, but if it’s the turbo-diesel engine, then the cause may be a pretty simple one. This engine has a habit of splitting the plastic trunking that takes the pressurised intake air from the turbocharger to the engine’s inlet manifold. If that happens, the air is free to escape to the atmosphere, and doesn’t make it’s way into the engine.

That’s why you’ll hear a noise like air escaping (because that’s precisely what it is) as well as a lack of power, because the engine is not receiving all the boost from the turbo. You’ll probably also notice that the car is blowing more black smoke than it should.

The fix is a new piece of plastic pipe that should be well within the abilities of any workshop to fit.