Starter Fluid to Check for Vacuum Leaks?

[350SL4spd]

Someone mentioned that you could check for vac leaks in a gasser by spraying starter fluid where you thought you had a leak. If you had a leak the idle would increase for a second.

Sound solids right?

I'm trying to diagnose a bad idle in my '75 450SL (D-Jet) & one thing I'm trying to eliminate is a leaking intake manifold gasket. I tried the starter fluid trick (carefully, mind you) & I didn't get a higher idle anywhere, but when I sprayed a bit (just a bit) in the intake itself the idle DROPPED. Is it flooding? On a drop of starter fluid? Doesn't sound right to me. Can someone give me a reality check?

Maybe a hot meal will set my head back on my shoulders...