vacuum @ idle increases as car warms up?

[jt15833]

cars been running solid for about a week now and i used to think i got 18 vacuum all the time now i notice sometimes its 18 sometimes its 16, but usually when hot its around 18. im going to to a compression check tomorrow just want to know beforehand if this is common, or a common issue or heard about before

[rico05]

Hmmm. I usually see 20 in/Hg unless the car is being a little b|tch.

[top_secret]

yeah I get 20-23 depending on temperature and idle speed.

[kapower06]

Im not sure why it would fluctuate due to temp. unless there was a leak somewhere that expanded or contracted with the temp. ma ka-e pulled a steady 23 in hg, no matter the temp.

[jt15833]

maybe i have a leak somewhere, whats the best way to check, let car idle and spray carb cleaner by all the hoses and listen for an increase in rpm?

[top_secret]

mine would idle higher when it was cold but its went away when I changed the battery, I think the old battery was nearly dead so everytime the car started the alt had to step it up a notch cause the batt was eating up the power.

[kapower06]

yea that method works well but, for small leaks you would have to saturate the area pretty good so it would ingest enough to change the idle...

[biosehnsucht]

if you open the throttle the vacuum decreases, for the same amount of consumed air - as the cold start solenoid closes off it would make sense for vacuum to change some, but since the cold start only lets in a tad more (doesn't take much to raise the idle ~600rpm or so in neutral) air you'd see only slight variations.

No need for leak consipiracy theories but these can also cause the same symptom.