Check all your grommets and bungs are in place. Also check the seal that seals the scuttle area from the engine bay is in good nick. The fresh air comes in from the scuttle area, hence the reason why it is sealed off from the engine bay.
If you have engine smells coming into the car, you really need to sort it soon. If you have the smallest exhaust leak that comes into the car, you can get carbon monoxide poisoning which is definately not good. Carbon monoxide is a colourless, odourless gas produce by the exhaust gasses, which are potentially lethal.
