2002, 180kms. Audi 3.0ltr petrol V6: surging at idle. The surge is rhythmic, varies by 200-300rpm, only seems present when the engine is warm, and can be replicated right up to 1,500RPM.
The surge gets worse if the oil filler cap is removed. Does this implicate or eliminate the PCV!
Ta.
Too much metric in engines today and not enough pushrods.
franc123,
Nov 29, 4:14am
May not be the valve itself but a vacuum leak could well be causing it, much of the vacuum hosing on this modern Euro stuff seems to be prone to rotting, collapsing and leaking when it gets old.Listen carefully for any hissing around the intake ports and pipework etc.
unclejake,
Nov 29, 4:18am
I had a good listen with my stethoscope but the results were inconclusive.
I am really keen to get some advice regarding the removal of the oil filler cap. In my mind it makes the PCV more likely to be at fault. but I could have that totally wrong.
mm12345,
Nov 29, 5:14am
I don't think so.If the PCV was blocked you might have other problems, oil leaks etc.But you should be able to remove and check the valve. The worsening of symptoms when taking the oil filler cap off might be related to airflow through a breather, but not indicating a faulty PCV valve. My guess is to find out what the car uses for idle speed control in the throttle body.Common system on many cars is for when the throttle is closed, there's a bypass duct with a stepper-motor controlled valve (IACV), metering air past the closed butterfly, with the ECU adjusting this air (and amount of fuel injected) to set a constant idle.The valves eventually gum up with gunk on many cars, causing erratic idle, low idle, surging. Can sometimes be cleaned simply by getting access to the throttle body opening (remove air hoses) and squirting carb cleaner down the IACV intake if you can see it.Otherwise, removal of throttle body might be needed to get access to clean it out. But start with the simple stuff, check that the PCV valve isn't blocked (even though I don't think it's the cause), as well as vacuum leaks, as suggested by franc123 above.
unclejake,
Nov 29, 5:17am
I was thinking that the PCV may be stuck open
mm12345,
Nov 29, 5:20am
I think if it was stuck open, then again it shouldn't affect idle speed, as at closed throttle/idle, manifold vacuum should mean it's "sucked" open anyway.
unclejake,
Nov 29, 5:28am
I will have a think about that more. Thanks for the thoughts.
In my brain a fluctuating idle could be caused by a vacuum leak, and if the PCV was stuck open then I would have a vacuum leak that got worse when I opened the oil filler cap.
I didn't have time to remove the PCV to check it properly. I guess that should be my next step.
These engines are drive by wire so it could be a throttle module too.
mm12345,
Nov 29, 5:34am
Yes, also could be O2 sensor.But perhaps those two would throw up a fault/check engine light. But for sure, check the PCV, vacuum leaks are apparently common on Audi, and google for info on the IACV, as these probably won't bring up check engine lights/codes.
unclejake,
Nov 29, 5:36am
Thanks. I will give Google a work-out later today.
snoopy221,
Nov 29, 6:58am
From post#1.The surge gets worse if the oil filler cap is removed
Doesn't mean the cap is SEALING when refitted U J. Get out the old 100 mph tape and seal the cap hole and see what that does to it. A lot Too much metric in engines today and not enough pushrods.
And sometimes **fussy** engines with leaking oil filler cap seals.
mm12345,
Apr 20, 1:44am
I don't think so.If the PCV was blocked you might have other problems, oil leaks etc.But you should be able to remove and check the valve to see if it's okay. The worsening of symptoms when taking the oil filler cap off might be related to airflow through a breather, but not indicating a faulty PCV valve. My guess is to find out what the car uses for idle speed control in the throttle body.Common system on many cars is for when the throttle is closed, there's a bypass duct with a stepper-motor controlled valve (IACV), metering air past the closed butterfly, with the ECU adjusting this air (and amount of fuel injected) to set a constant idle.The valves eventually gum up with gunk on many cars, causing erratic idle, low idle, surging. Can sometimes be cleaned simply by getting access to the throttle body opening (remove air hoses) and squirting carb cleaner down the IACV intake if you can see it.Otherwise, removal of throttle body might be needed to get access to clean it out. But start with the simple stuff, check that the PCV valve isn't blocked (even though I don't think it's the cause), as well as vacuum leaks, as suggested by franc123 above.
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