"how can we check for intake vacuum leaks?"
yeah the way I find vacuum leaks on carb OR MPFI intake manifolds is clean and easy with no mess. get a propane torch,or you can use your oxy-acetolene welding torch if you have one, (DON,T TURN THE OXY tank/or valve ON)
(DONT LIGHT IT) just SLIGHTLY open the valve so its allowing gas to flow at a low voluum,start the engine and let it idle at the lowest speed you can then place the tip of the UNLIT torch at any suspected vacuum leak and listen for the rpms to increase and watch the tach, gas flowing into a vacuum leak will increase engine speed.
look for loose or missing vacuum hoses, cracked or broken power brake connections, emmisions system hoses that are loose, vacuum connections to the trans or ignition, loose connectors missing or loose bolts cracked hoses missing assessory connections etc.
SPRAYING almost any flamable mist to find vacuum leaks is a big NO!NO!
simply because it tends to be BOTH a fire hazard AND leaves a film in many cases that attracts dirt or harms the finnish on the intake and components,and in some cases hurts plastic connectors and hoses, PLUS it is not precise enought, a torch tip can locate the leak to within an inch or so, a blast of engine start ether (start fluid) will tend too give you the AREA but seldom limit the results to less than about 1/4 of the engines intake because you can,t contain the mists flow dirrection well
yeah! we all did that, but this has proven to be a better & more effective,cleaner and safer method