ECU vacuum hose

I've got a new vacuum hose on order, but I was wondering what I could do to prove whether or not the ECU is sensing the right level of vacuum or not?



If everything in that department is behaving correctly, what effect should I notice if I were to disconnect the vac hose from the ECU? Will the idle speed be affected, will it just make the car run poorly, or will it do something/nothing else that is easily discernable?

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