-7 psi at idle?
 

I just got my boost vac gauge installed in the car, and I noticed that I was getting -7 psi for idle. That is about 14.25 inches of mercury, and I was wondering if this was normal, of if I need to be checking for leaks.

That's a little low, it should be 18-20" of mercury. Is that at a hot idle- such as 7-800rpms?

Wait, I see that your car is only 600cc- is it a 2 cylinder? If so, maybe 14" is acceptable.

it's a 650cc 4 cylinder turbo. it's about the same at warm idle

Is it idling smooth? Ignition timing that is retarded can cause low vacuum at idle. Or maybe your boost gauge's needle isn't calibrated correctly with the numbers on the dial.

My '88 Escort holds about 20-21 inches vacuum at idle hot or cold.

that's pretty low for idle. things like vacuum don't change much for engine size. briefly I thought it might be the turbo but it shouldn't be doing anyhting at idle. I'd start by checking for vacuum leaks and that the throttle plate is closing fully.

Try reving it up and see if the vacuum increases. An engine that small doesn't generate a lot of vacuum at idle because of all the losses moving four small pistons but reving it up should make a little more vacuum.

vacuum increasedto -9 psi, and goes to -10 on a hill.

Is it a cheap brand of gauge? Find something you can check it against. Like a vacuum diagnostic tool.

Not sure if that is correct because usually vacuum is measured in inches of mercury except in Turbo gauges.

for the inches of vacuum multiply by 2.0293855020699732121113726763536

so 10spi is about 20.2 inches of vacuum sounds about right.

500mm vacuum = 9.7 psi

Atmospheric pressure is about 15psi and that is about 30-32 inches of mercury about 2 to 1