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Thread: Car revving itself on idle ?

  1. #1
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    Car revving itself on idle ?

    Hi All

    Had the problem the other day I drove home from work and when I pulled onto my drive I let it idle a few mins like normal and the revs increased and went back down so I thought I might of twisted the mat or pressed the accelerator so moved mat out the way and it did it again and went upto 1500rpm and continued fluxuating.

    Next day was fine until again I got home, so it only seems to do it when its warm, also have noticed my mpg has gone down, done a search on here and it points to a breather problem so I have checked the PCV valve and that seems fine, I have also tried removing the oil cap when the problem occurs and it is very difficult as its under a vacuum.

    Where do I start looking or common failures ?

    Thanks in advance

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  3. #2
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    MAF?

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    Mates car had this. Turned out to be the fuel flow valve.
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    Is it a petrol or diesel?

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    Don't think its MAF as this wouldn't cause a vacuum,

    Thanks- will look into fuel flow valve

    The car is a 2006 Audi A3 2.0t petrol 200bhp

    thanks for responses

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    Just been doing some googling and Broadsters solution has come up a few time with all the same symptoms and part is very cheap and easy to fit which I do like lol.
    going to get one order and fitted and go from there
    Thanks again

  8. #7
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    do you have the part number and price that you would like to share, so it's handy if i have to replace it or anybody else
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    Im away this week on a course but am back Friday so will get one sorted then hopefully and will post part no up and price
    S. likes this.

  10. #9
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    Cant the pcv also cause this ?


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    Quote Originally Posted by phil76 View Post
    Cant the pcv also cause this ?
    Have taken pcv off and one way valve is fine

    thanks craig

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    Got back and have got the n80 valve, part no is 06E 906 517A

    took 15mins to fit and was easy as it gets

    time will tell if it has worked and I will update in a few days

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    The n80 valve has made a difference however the fault is still there and now has brought the engine management light in saying. System to lean bank 1

    any ideas as getting stuck now

    thanks Craig

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    Bump

  15. #14
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    You've got an air leak post maf sensor.

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    On the boost pipes, As thought in was vacuum related?

    not saying your wrong lol just confirming I I can check the right bits :-)

    Thanks Craig

  17. #16
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    It could be you boost pipes - basically you need to check all the pipes from the maf sensor to the throttle body - the way the diagnostics system works is by measuring the airflow going through the maf sensor and comparing that value to a calculated value flowing through the throttle body, now if there is a difference in airflow between the 2 then it will throw up a fault code.

    During idle or part load running the system will be in vacuum so it will be drawing in air after the maf sensor meaning that the engine is still getting the same amount of air however the maf hasn't measured some
    of this air.

    I have seen this issue many times during my 8yr career in engine development on Bosch ecus.

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    Thanks for your response, I will have a look and report back
    thanks Craig

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    Just jacked the car up and the two boost pipes connecting to the intercooler were both not connected very well so have cleaned them up and reconnected and reset engine light so wait and see what happens tomorrow

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    Quote Originally Posted by S3_Mat View Post
    MAF?
    You may be right with this being the problem, I disconnected the maf and the car no longer goes crazy on idle, it does still rev a tiny bit and also the revs are slower to return to idle but assuming this is because the car does not how much air is going into the engine?

    So guessing replace the maf?

    thanks craig

  21. #20
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    Sorry to dig up an old thread, but I've been scouring this forum and a lot of others but no one seems to have the same probem as me lol :/

    My car is a 55 (06) plate A3 1.9tdi, BKC engine code with 120k on the clock.

    I've realised when my car is idle my revs will rise from approx 850-900 rpm and sit on 1000rmp (just a little above). This can be from a cold start, when i start the car first thing in morning the revs will rise and as the engine warms up it'll auto-rev to 1000rpm every time i sit at idle. When the revs do rise if i press the accelerator it'll drop back to 850rmp only to rise a few seconds later.
    Ive also realised every time the car revs the fans kick in for about 30-45 seconds and then stop but the revs will stay at 1000rpm. I have checked battery voltage and its not a bad battery causing it.

    Theres no codes apart from glow plugs which i don't think should effect the rpm, so not sure what it is, any help would be much appreciated lads. Thanks

 

 

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