Question

which idle speed if the vacuum pressure gauge read​

Answer 1

Answer:

Idle vacuum for most engines is about 18 to 22 in Hg

Explanation:

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Idle vacuum for most engines is about 18 to 22 in Hg, but some may produce only 15 to 17 inches at idle. ... If vacuum is steady at idle but lower than normal, the ignition or valve timing may be retarded. Low compression, an intake leak or tight valves also can cause low vacuum at idle

Hope this helps