I have tried butane, cigarette smoke, etc. If the leak is large enough, those work. Usually, it is the smaller leaks that cause MPG problems, the engine management adds fuel to make up the difference.

There is no easy way. If you cleaned the PTC nipple on the intake before the turbo, make sure it is seated tightly. As for the intake manifold, all you can hope for is that the bolts are all properly torqued, and you started from the inside and worked your way out.
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Keeping it running is better than buying new