# Remove oil cap = rough idle/ misfire... Normal?



## Fast VW (Sep 24, 2002)

Sorry if this has been discussed but I cannot find a definitive answer by searching. I am relatively new to the MKV platform so I do not know if this is normal. I have an 08 rabbit and when the car is at idle and I unscrew the oil cap, the car idles terribly and misfires. Obviously it is creating a vacuum leak but is this normal? My MKIII doesn't have vacuum present under the oil cap.

Thanks!


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## [email protected] (Aug 18, 2011)

Sounds like your PCV is probably torn. The PCV is inside the valve cover; within that hump to the left of the oil cap. 
If the PCV does have a tear, it will create a vacuum leak within the valve cover which often results in a lumpy, erratic idle. 

When you attempt to remove the oil cap while the engine is running, is it difficult to remove? That's a tell tale sign the PCV is busted.
A couple of codes it pop up intermittently, but I don't know what they are off the top of my head. I'll have to report back.


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## mk6matt (Jan 26, 2013)

There is also a line to the crank case that could cause that same vacuum I believe. I think that's where the vacuum is coming from.


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## Fast VW (Sep 24, 2002)

The oil cap is not difficult to remove when the engine is running and the car runs fine with the cap on. I also scanned it with vagcom and have no codes.


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## Fast VW (Sep 24, 2002)

I have been reading on some other forms that this is actually normal and the pcv is only faulty if the oil cap is difficult to remove.

Can anyone confirm this??


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## Fast VW (Sep 24, 2002)

Same thing happens when I remove the dip stick. Anyone?


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## mk6matt (Jan 26, 2013)

Removing the dipstick is the same as removing the oil cap. Both are connected to the crankcase. Its likely the crankcase or valve cover vent which create a vacuum in the engine. As far as I know its normal.


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## nikolasmouzourou1 (4 mo ago)

[email protected] said:


> Sounds like your PCV is probably torn. The PCV is inside the valve cover; within that hump to the left of the oil cap. If the PCV does have a tear, it will create a vacuum leak within the valve cover which often results in a lumpy, erratic idle. When you attempt to remove the oil cap while the engine is running, is it difficult to remove? That's a tell tale sign the PCV is busted. A couple of codes it pop up intermittently, but I don't know what they are off the top of my head. I'll have to report back.


 what is the pcv you’ve mentioned? Is it the head gasket?


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## ChefroA6 (Dec 3, 2020)

nikolasmouzourou1 said:


> what is the pcv you’ve mentioned? Is it the head gasket?





[email protected] said:


> The PCV *is inside the valve cover; within that hump to the left of the oil cap*.


@nikolasmouzourou1 :
If your question was indeed for real, then your answer was already in this thread.
How VW Parts Fail ~ 2.5L Valve Cover with PCV Valve - YouTube


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## CraigH (Jul 22, 2018)

That is also the case on my 2017 Beetle.  It happened during an oil change - started the car and very rough idle. I feared for my automotive service capabilities. 

I had left the cap off with the intent of getting the oil level properly set. Installing the cap stopped the rough idle.


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## RadioCow (Jul 12, 2020)

If it idles rough when you remove the cap you're fine. Your PCV is torn if the oil cap is almost glued to the engine.


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