Idle changes when removing oil cap or dip stick

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06-25-07, 02:47 PM

mthree0

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Idle changes when removing oil cap or dip stick

Hello,

I have a 1993 Mazda MX-3 GS that I am selling. A possible buyer took a look at it and noticed that the idle changes when removing oil cap or dip stick? Is this something to be concerned about? I would think that this is not a problem given the change of oil pressure. The car does not stall, but rather the idle speed changes and comes back to normal in a few seconds after the oil cap/dip stick is removed. As far as I know, there is nothing wrong with the car.

Thanks,
Mark

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06-25-07, 03:55 PM

New guy

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It's perfectly normal, by removing the oil filler cap and or dipstick while engine is running, you are creating a vacuum leak which will effects on engine idling.

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06-25-07, 06:44 PM

the_tow_guy

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Vacuum leak via the PCV system as New Guy indicates. I have never heard of anyone looking to buy a car (or for any other reason) remove either the oil filler cap or dipstick while the engine was running.

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06-26-07, 04:03 AM

New guy

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Looking for "blow-by" may be.

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06-26-07, 05:50 AM

the_tow_guy

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I suppose, but there's always going to be air movement with the engine running, so quantifying the blow-by amount would be tough, I think.

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