Author Topic: Can a vacuum leak mask failed PCV dipstick test?  (Read 384 times)

Offline toerag

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Can a vacuum leak mask failed PCV dipstick test?
« on: October 12, 2020, 05:16:00 PM »
So I just finished the NC500 in my GTI and had a great time definitely would recommend. After putting around 1.7k miles on the trip on the motorway back I noticed a distinct lack of oomph overtaking with a fully loaded car and a rough idle. Instantly thought PCV valve and did the fabled test at the services (to calm my worried heart) and pulled the dipstick.
The engine was sounding very rough after but the initial idle made it hard to tell. Anyway I got back to London and in the inevitable traffic my car was revving of its own accord up until 2000 rpm and back down. Once the rain had stopped the next day I pulled the hose of the manifold side of the PCV valve and gave it a blow. My PCV had definitely gone but the dipstick test was still causing a rougher idle. Anyway new PCV valve has gone on and the cars idle is smoother but is much higher and once the engine is warm it is still revving by itself. I am also hearing a distinct hissing noise that was definitely not present before the new PCV went on... :thinking:
Do I have a Vacuum leak? What would your next steps be? Pay a mechanic for a smoke test? Sadly I do not have a scanner.
Thanks in advance
H

Offline colesey

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Re: Can a vacuum leak mask failed PCV dipstick test?
« Reply #1 on: October 12, 2020, 07:04:46 PM »
Sometimes there have been issues with the dipstick itself, where the seal at the collar deteriorates with age, so  maybe have a look at that first.

Offline titchy

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Re: Can a vacuum leak mask failed PCV dipstick test?
« Reply #2 on: October 13, 2020, 09:12:00 AM »
I had a similar problem smoke test failed to spot it turned out to be a housing beneath the vac pump which is split into carrying  water and vacuum  when it was replaced another plastic pipe was also broken causing a vac leak the part was £18

Offline ROH ECHT

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Re: Can a vacuum leak mask failed PCV dipstick test?
« Reply #3 on: October 14, 2020, 09:04:37 PM »
It could still be the PCV...in that you may have installed the Rev.-P PCV with an open rear breather tube. If its rear breather tube is open...you need Rev.-R PCV; 06F 129 101 R...as it has a check valve to seal and vacuum. If you have installed the correct PCV and have an open rear breather tube...then it may be the rocker cover itself is no longer sealing the EVAP and PCV passages inside.

But, it is possible there is a leak somewhere. You don't have VCDS so someone else will need to test for leaks by looking at STFT (MB 033) and LTFT (MB 032) data for you. But yes, it probably has a leak or more.

Or...you just give it a thorough inspection yourself. Or make up your own smoke tester and give that a try.

Another slim possibility would be the throttle-body unit is failing.
Having someone pull up its DTC's would be helpful...but it doesn't code for a leak unless fuel trims have exceeded 25% rich or lean.
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Offline toerag

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Re: Can a vacuum leak mask failed PCV dipstick test?
« Reply #4 on: October 21, 2020, 04:30:46 PM »


Or...you just give it a thorough inspection yourself. Or make up your own smoke tester and give that a try.

Another slim possibility would be the throttle-body unit is failing.

Dipstick looks good
I will definitely look into the PCV but to my ear the hissing sounds like its coming from the lower right side of the engine.
I am all about trying to inspect it myself. I'll look into a DIY smoke tester.

Thanks!

Offline ROH ECHT

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Re: Can a vacuum leak mask failed PCV dipstick test?
« Reply #5 on: October 22, 2020, 12:57:07 AM »
The literal right side___or facing it right side? Can you post/share with us a vid of where you hear it most?
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Re: Can a vacuum leak mask failed PCV dipstick test?
« Reply #6 on: October 22, 2020, 08:00:49 AM »
You can also check the intercooler hoses and provably you will see a lot of oil there... check the rocker cover specialy near the oil inlet your can spry water there and check if you see bubbles.