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When I remove oil filler cap while the engine is running at idle, the RPM drops and the engine nearly die. Is it normal ? (V6 2.5L)
 

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I'm pretty sure it's normal; my 95 does it as well. It's somewhat the same as creating a vacuum leak. Pulling the dipstick will do it too.

Tyson
 

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}) really?.... i wonder why my 4 doesnt do that... or why the 6 does it... ive never heard of a car doing that...
 

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I guess it's normal, a friend of mine bought a Probe GT and it dies when you take the cap off... havent checked if my 6 does that... probably does, i'll check tomorrow...
 

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Yup, it is creating a vacuum leak. Same with the dipstick. Mine does that as well. Of course, why would you want to remove the oil filler cap while the engine is running anyways. I am not a big fan of having oil all over the place.
 

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By removing your cap while the engine is running is one easy way to see if your rings are worn out. If they are, you'll feel a irregular amount of air coming out of the filler hole.
 

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it's very good

if the engine die or drop idle while removing the cap it means engine has very good compression
It's fast and simple evaluation of engine condition when buying used car
 

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The engine dies because of the way the VAF works, not solely because doing so creates a vacuum leak. The VAF operates on the principal of a pressure drop across it, which causes the plunger to move back, allowing air to move through and into the engine. If you take a pressure reading on either side of the VAF with the engine idling, you'll see that the "throttle body" side is a bit lower than the "air cleaner" side.

When you open the oil cap, you're allowing air into the engine. On the top of both valve covers are tubes that connect to the big breather tube on the back of the throttle body elbow. Air normally flows into that breather, through the engine and is drawn out via the PCV valve into the intake. All of this air is supposed to be all measured by the VAF; both the air entering the throttle body and the the air bypassing it and going the PCV route.

When you open the oil cap, you basically vent the entire system to the atmosphere, including the volume behind the VAF. As a result, the VAF will close and the PCM sees this as a reduction in airflow. It'll reduce the fuel amount, the engine will stumble and likely stall. Not always, but most.

My V6, with the MAF in place the VAF, runs quite happily with the oil cap off, spewing oil over everything in the process.
 

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makes sense... good ol 4 bangers with the MAF...
 
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