# 2002 Passat Rough Idle with Oil Cap Removed



## jcmac (Nov 13, 2007)

After just having changed the oil I ran the engine without the oil filler cap on. It ran very rough. Is this normal? No other car I have owned did that. Even my Audi 2.7T does not do that.
Could it be that the crankcase vent system has been hooked up wrong or is in need of service?
Thanks!


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## wigsjet92 (Nov 8, 2002)

*Re: 2002 Passat Rough Idle with Oil Cap Removed (jcmac)*

Did it run smooth after a little while or after the cap was reinstalled?


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## jcmac (Nov 13, 2007)

*Re: 2002 Passat Rough Idle with Oil Cap Removed (wigsjet92)*

Yes, after replacing the cap on the valve cover the idle did smooth out. I found it odd though that my Audi 2.7T did not experience any roughness at all when the same cap was removed from the valve cover. 
The two engines have their differences but they are about 75% the same. Again is this a problem to do with the internal venting of blowby or a normal expected condition..


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## jcmac (Nov 13, 2007)

It continued to run roughly for atleast 1 minute at which time I then placed the cap back on and it instantly became much smoother. I should mention that it was smoother than that a while ago but not really smooth recently.


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## passatCA (Jun 8, 2007)

*Re: (jcmac)*

Just had exactly the same issue this past weekend with my Passat V6, upon start-up with the cap off it ran like it was misfiring and then with the cap on it sorted itself out. 
Anyone come up with any ideas?


_Modified by passatCA at 10:05 AM 11-19-2007_


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## jcmac (Nov 13, 2007)

*Re: (passatCA)*

I have just been informed by the dealer that the behaviour we have experienced is completely normal. Apparently the engine has a closed vent system and needs the oil filler cap attached to operate properly.
Cheers


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## passatCA (Jun 8, 2007)

*Re: (jcmac)*

Thanks for the info Jcmac, i was wondering if i was going to have to spend more money...


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## Roger2Texas (Mar 12, 2008)

*Re: 2002 Passat Rough Idle with Oil Cap Removed (jcmac)*

Same exact thing happened to me yesterday after changing the oil on my 07' Jetta 2.5.. thought I had screwed something up after putting the cap back on realizing that it was because of the cap after all!! I try to be so careful since repairing these things is extremely costly!!


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## spitpilot (Feb 14, 2000)

*Re: (passatCA)*


_Quote, originally posted by *passatCA* »_Thanks for the info Jcmac, i was wondering if i was going to have to spend more money...
 Any one with 60K and above on their 30V V6 has got to take a hard look at their PCV system...I started seeing some leakage of oil at the cam adjuster seals...I read in Audi World Forums that Audi had put out a tech bulletin saying to replace the PCV hoses and "suction pump" B4 doing any replacement of these seals/valve cover gaskets etc....So I changed the big PCV hose (loops around the engine to the right valve cover) the small hose behind the engine (goes under the throttle body so you have to remove that to change hose..but then you can clean the TB so it not so bad) and the "suction pump"..a little "Y" shaped piece of plastic that controls the amount of vaccum in the PCV system...after changing these the leaks stopped! Parts aren't super expensive..about $100 for all..so yes you might have to spend some more money!


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