Does propane change with age? The web says No, but....

I have a can/bottle of propane that is at least 10 years old.

I'm using it as one of several ways to find the vacuum leak in my car.

I used it 2 years ago and got nowhere, but I'm being more diligent this
time. I have an old valve to which I've added some windshield washer
tubing, so that I can reach anywhere (although the curve that won't go
away from the tubing makes it hard to get to some places).

But I'm used to propane having a strong, distinctive, maybe pungent
smell, even just a whiff of it, and this stuff, Berzomatic brand. 14oz.
fwiw in a tubular blue can (shaped like a salami), has barely any smell.
In fact I wasn't even sure the valve was opening. Only because frost
was forming on the valve (that screws to the bottle) was I sure
something was coming out.

Also, when I didn't find a leak, I removed a small hose from the air
cleaner box and I attached the hose from the propane bottle. Barely any
change in the sound of the engine. Wouldn't have noticed it if I were
not listening for it. Should I have attached it somewhere else? Or
is propane just not a good test substance? I also have MAPP gas if
you think that would work better.

This is somewhat complicated because these Toyota engines idle at
2000rpm to start and slow to 750 after 3 or 4 minutes.

So I'm rushing to test while the engine is cold and it's all the time
lowering engine speed and changing the sound it makes anyhow.



40 years ago, I had a car that stalled if you didn't give it extra gas
until it warmed up some. AFAIK, that car was considered in need of
repair. But now it seems, with a microprocessor that can start with a
fast idle (better or faster than the fast idle cam) and lower it later,
Toyota just covers up this problem by providing 2000 rpm idling, instead
designing the engine to not have the problem. Am I too cynical? Do
other makes of cars do the same thing?