Hi ACD,

Two ways to check for a vacuum leak. You can visually inspect the suspected hoses or, even better, remove them so you can flex them and check for cracking, splits etc.

Alternatively you can use a spray such as WD40, or lighter refill gas with an aerosol nozzle. Spray the suspected area - if the revs rise slightly then there is a vacuum leak through which this flammable gas is being drawn. Obviously, take care whilst doing this - no one wants your face looking like the innards of a Mickey D cheeseburger!

The idle air control valve is worth checking with the symptoms you describe but don't forget the basics eg, plugs not fouled, dizzy cap and leads in good condition etc.

Regards,

Big Rich.

PS - If it's any help I have an aftermarket TIM Superdash vacuum guage on my car. At idle the needle sits at the 1 o'clock position, 3 o'clock on the overrun and anywhere from 7 to 11 o'clock whilst driving, depending on how much right foot i'm giving it.
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The Volvoboy...he never grew up!