# High Revving when idle...



## datamonkey (Jan 23, 2012)

When coming to a standstill out of gear and idle, my TT's engine is revving between 800-1600rpm at random with my foot totally off the accelerator...? It generally sits around 1000rpm but does fluctuate.

This has just started all of a sudden and the engine sounds fine when running.

Got it booked in at my local garage in a few days time but just wondering what the mechanically-minded on here might guess it could be?

Thanks! :?


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## bomasspot (Mar 13, 2011)

More than likely to to be the PCV. Not too much from Audi.


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## datamonkey (Jan 23, 2012)

bomasspot said:


> More than likely to to be the PCV. Not too much from Audi.


Thanks. Is that to do with the coil packs?


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## igotone (Mar 10, 2010)

datamonkey said:


> bomasspot said:
> 
> 
> > More than likely to to be the PCV. Not too much from Audi.
> ...


Nope - nothing to do with the coil packs it's most likely your Positive Crankcase Ventilation Valve. What it does is recycle your burnt gases by diverting them from the exhaust manfiold back into the cylinders for another combustion cycle and so reduces emissions. Good explanation HERE...

http://auto.howstuffworks.com/positive- ... system.htm

Just be aware it could be a leaky or loose hose on the manifold too. I THINK that if you remove the oil filler cap with the engine running and the engine starts to run rough it's a good indication of a fault with the PCV.

Something to get looked at ASAP. You could get a CEL light on the dash pretty soon.


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## datamonkey (Jan 23, 2012)

igotone said:


> datamonkey said:
> 
> 
> > bomasspot said:
> ...


Thanks for your help guys. Fingers crossed it is just the PCV and not something more costly!

I will give the oil filler cap thing a go and see how the engine responds but it seems a bit rough already!


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## igotone (Mar 10, 2010)

The thing is that the PCV valve diverts already spent gases into the cylinders for a second ignition phase, inevitably leaning out the mixture somewhat. This is going to be most noticeable when moving slowly with little or no accelerator input which is why the engine is surging when stationary - basically it's hunting for a richer mixture so you may not notice much difference removing the oil cap if it's already surging.


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## bomasspot (Mar 13, 2011)

Removing the oil cap didn't work for me. Took mine to Audi and £140 lighter problem fixed. If I knew in the beginning how easy it was to replace I would have done it myself [smiley=bigcry.gif]


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## datamonkey (Jan 23, 2012)

igotone said:


> The thing is that the PCV valve diverts already spent gases into the cylinders for a second ignition phase, inevitably leaning out the mixture somewhat. This is going to be most noticeable when moving slowly with little or no accelerator input which is why the engine is surging when stationary - basically it's hunting for a richer mixture so you may not notice much difference removing the oil cap if it's already surging.


I tried the oil cap exercise and the engine didn't like it! 

It was spluttering before then when I removed it spluttered even more...

I'm not going to drive it until Saturday morning when it's booked in.

Thanks again..


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## datamonkey (Jan 23, 2012)

bomasspot said:


> Removing the oil cap didn't work for me. Took mine to Audi and £140 lighter problem fixed. If I knew in the beginning how easy it was to replace I would have done it myself [smiley=bigcry.gif]


I looked on YouTube and even though the job does look easy I'm not sure I'll do it myself.

I'm a complete noob with engines and I'm still not 100% it's the PCV - though it probably is from what you chaps have said. Plus there doesn't seem to be many on ebay and those that are on there are probably dodgy copies from China!


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## Sebbyp (Oct 16, 2014)

Hi

Have a similar problem with my TT, idle is a bit rough and revs sit around 800 and sometimes increase slowly to 1100. Other times it will randomly jump to 2000 then fall back down again.

Have took the inlet hose off the PCV and blown down it with no air passing. Does this mean the PCV is ok? Also took oil filler cap off while running and engine nearly stalled and idled a lot worse. Also tried dipstick and same. The cap was fairly easy to take off.

Had code P-0171 System too lean.

Now after a week or so had a bunch of other codes:

p1095 p2187 p0507 p2279.

Going to get it smoke tested next week but any other advice would be much appreciated.


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## paultts (Apr 27, 2013)

Hi Datamonkey,

I just saw your post this evening, after I had posted a similar problem yesterday "Uneven idle and backfire on 1st-2nd gearchange" (on my TTS). Did you get it resolved, and if so, could you let us know the cause ?

I don't know where to turn next, as the audi dealer more or less said if my problem continues, leave it with them and they will randomly replace bits until it is fixed - sounds expensive ! :?


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## Stolberg (Oct 4, 2013)

I had been experiencing a rough idle for sometime, with no idea what is was. Then during a long trip, stopped at lights, my engine began to rev upto 200rpm and back down.

Thanks to this feed, I bought a new PCV valve and fitted within 10 minutes.

Both rough idle and revving has dissappeared. A simple and quick fix, for waht seemed to be an expensive and complexed issue.
Cheers!


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## Sophus (Apr 26, 2013)

I may be wrong, but to me it seems Igotone's first explanation of the diagnose test of removing the oil cap can easily be misunderstood.

To my understanding:
Removing the oil cap or dip stick on a perfectly healthy engine will make it run badly and splutter. That is normal.

However, if it already runs badly because your pcv or hoses are at fault, the test of removing dipstick or oil cap will not make much difference. That is an indication that you need to change pcv or start looking for leaks. Correct?


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## TT-driver (Sep 14, 2010)

Correct.


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## Sebbyp (Oct 16, 2014)

Sophus said:


> I may be wrong, but to me it seems Igotone's first explanation of the diagnose test of removing the oil cap can easily be misunderstood.
> 
> To my understanding:
> Removing the oil cap or dip stick on a perfectly healthy engine will make it run badly and splutter. That is normal.
> ...


I had this issue and doing that test made the engine run a lot worse. My idle was fine when cold it wasn't till warm when it began to feel rough and vary the idle revs. So I had a faulty pcv and removing the oil cap made a lot of difference, it would nearly stall and idled a lot worse.


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## Sophus (Apr 26, 2013)

So, the test still got your car running much worse but your PCV valve was still leaky. 
Possibly your leaky valve didn't leak that much?


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## Sebbyp (Oct 16, 2014)

Sophus said:


> So, the test still got your car running much worse but your PCV valve was still leaky.
> Possibly your leaky valve didn't leak that much?


Possibly yes. It was pretty bad at over revving and throwing up codes though! Moral of the story is if you have these symptoms its worth doing first as its on the cheaper options and seems a common fault. Even if it seems to pass this "test"


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## Stolberg (Oct 4, 2013)

It is a £40 job to change the PCV, which literally takes take 10 minutes, to remove the engine cover, two pipes and several screws.

I'd recommend giving it ago before taking to a garage.


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## jcdenton115 (Mar 24, 2019)

I too had a similar issue with the revs going up of their own accord Sounds Like a complete noob mistake I was sure it was my PCV that was broken and was looking for a garage. however took another look under the bonnet and my dipstick was about 3 cms too high pushed it back in and bobs your brothers mother once again running like a dream !!!!

Woops!


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## 5 iron (Sep 20, 2021)

jcdenton115 said:


> I too had a similar issue with the revs going up of their own accord Sounds Like a complete noob mistake I was sure it was my PCV that was broken and was looking for a garage. however took another look under the bonnet and my dipstick was about 3 cms too high pushed it back in and bobs your brothers mother once again running like a dream !!!!
> 
> Woops!
> Hi everyone,, i had the problem when the engine was idling on my tts, it went up to 1600 rmp then drop down again, i tried the dipstick and pushed it down about an inch, and the problem stopped😄 The week before i had checked the oil level and not pushed the dipstick all the way down. Thanks to this forum it solved the probmem. Many thanks


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## AnabolicStewie (Jul 30, 2019)

jcdenton115 said:


> I too had a similar issue with the revs going up of their own accord Sounds Like a complete noob mistake I was sure it was my PCV that was broken and was looking for a garage. however took another look under the bonnet and my dipstick was about 3 cms too high pushed it back in and bobs your brothers mother once again running like a dream !!!!
> 
> Woops!


Thanks for posting this. I had done the PCV and was ready to book into a garage - then after reading this I checked the dipstick. What a dipstick I am - it was the exact same thing! Back to normal now s thanks again.


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## diane18wood (6 mo ago)

bomasspot said:


> More than likely to to be the PCV. Not too much from Audi.


I took mine to garage said it could be charcoal canister....when I said others are saying PCV valve he said we can try that first I don't want to waste my money any ideas please


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## diane18wood (6 mo ago)

I took mine to garage said it could be charcoal canister....when I said others are saying PCV valve he said we can try that first I don't want to waste my money any ideas please


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## Wolvez (Jun 22, 2018)

Buy a scantool if you don't want to waste money. It's easy to diagnose the problem when you have live data.


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## diane18wood (6 mo ago)

Wolvez said:


> Buy a scantool if you don't want to waste money. It's easy to diagnose the problem when you have live data.


Thanks beyond my scope 😞


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## Hoggy (May 8, 2002)

diane18wood said:


> Thanks beyond my scope 😞


Hi, If you have an android phone/tablet OBD Eleven is simple to use, plug in & press a button, £35 saved the 1st time you use it.








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Hoggy.


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