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low vacuum?

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Old Jun 5, 2005 | 01:06 PM
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Svelte_SS
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From: TEXAS
Car: 1987 Monte Carlo SS
Engine: 5.7L TPI
Transmission: 4 spd auto
low vacuum?
I hooked up a vacuum guage to my plenum yesterday and was reading a steady 12 Hg at idle.

Is this low? Isn't it supposed to be 17-20 Hg?
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Old Jun 5, 2005 | 07:29 PM
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8Mike9
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From: Oakdale, Ca
Car: 89 IrocZ
Engine: L98-ish
Transmission: 700R4
For a stock to mild cam it's low.

If you don't have a vacuum leak somwhere, could be the throttle blades are too far open at idle.
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Old Jun 6, 2005 | 02:04 PM
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Svelte_SS
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From: TEXAS
Car: 1987 Monte Carlo SS
Engine: 5.7L TPI
Transmission: 4 spd auto
So how do I fix that? Just re-adjust my minimum air?
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Old Jun 6, 2005 | 07:15 PM
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8Mike9
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From: Oakdale, Ca
Car: 89 IrocZ
Engine: L98-ish
Transmission: 700R4
Yes, should set minimum air to spec...not to control idle. The IAC should control idle speed to target RPM once min air is set.
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Old Jun 7, 2005 | 02:26 PM
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Svelte_SS
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From: TEXAS
Car: 1987 Monte Carlo SS
Engine: 5.7L TPI
Transmission: 4 spd auto
so what should my vacuum be at idle?
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Old Jun 7, 2005 | 03:37 PM
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8Mike9
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Joined: Jul 1999
Posts: 5,183
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From: Oakdale, Ca
Car: 89 IrocZ
Engine: L98-ish
Transmission: 700R4
Stock motor at sealevel, should be 18+ in/hg.
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