With as much polished and powdercoated stuff as I've got under the hood, flamable corrosive chemicals are straight out of the question. If I had a ragged out 94 Ford Probe, I wouldn't care.

Using a fuel source is okay on the intake manifold and throttle bodies of NA cars while they're idling if you know the problem is around there, but it's not a good way to test a turbocharged or supercharged car, or to diagnose its overall health because there are just SO MANY PLACES you can leak boost from... (and probably do) that it would be really expensive and messy to buy all the cleaner you'd need.

The bad part about using a fuel source as a leak finder aside from it being dangerous is that on a turbo car, leaks can happen in only one direction. Meaning, when you're under boost, and only above a certain pressure... you can develop a leak. It also won't tell you that you'd blow your intercooler pipes off at X or Y pressure, or if your vacuum lines are punctured or cracked. But it will raise the idle when it's sprayed in the general neighborhood of the problem, and a lot of skilled mechanics (that know what to look for on any given engine) get by with that added-fuel trick. One of my 20+ year experienced friends told me to use propane... and if you ever thought carb cleaner was flamable...