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Uneven idle and vacuum forming

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  • [Corsa D] Uneven idle and vacuum forming

    Hi all.
    My Corsa idles unevenly has vacuum build up - really pulls hard on the oil cap and slightly on the dipstick - it's not showing any faults at the but is heavier on fuel and doesn't have the same power as it used to have. It has also developed a squeaky noise from the engine when warm.
    So far I've only checked the rocker cover valve which seems fine. Any help would be greatly appreciated. Thanks

  • #2
    Welcome to the Forum.

    Your car has positive crankcase ventilation, which is designed (amongst other things) to prevent oil leaks, so the should in fact be a vacuum there.
    Pressurisation in the crankcase can indicate piston blow-by, so at least you are not suffering from that.

    My standard question with problems like yours is, "Is the car anything like due for a FULL service? - If so, that alone may well overcome all of your problems.
    A full service would (or should) include a new air filter element and new spark plugs, either of which could account for the poor fuel consumption.

    It is difficult to suggest what the squeak might be, as there are a few possibilities - maybe you could catch it on a video and post it for us, or a mechanics stethoscope might locate it, not expensive, but you can improvise by placing one end of a length of dowel (or even a long screwdriver) on the suspected area, and the other end into your ear.
    Possible culprits include the coolant (water) pump, alternator or belt tensioner pulley.

    If a service is not due, or does not solve the problem, I would suggest that, rather than fit parts that you may not really require, you have the fault codes read - there may be some obsolete codes in there, so it is better to clear (delete) them and see if any new codes return after a short while, this/these would likely indicate your problem.



    • #3
      Thanks for your comment.

      The car has 131,000 miles with a full service history last complete filter and plug change at 122,000. we usually change the oil and filter every 10,000 so that's due soon. I ordered a PCV valve yesterday as I can blow through the existing one.
      I will check and delete any existing codes tonight and see if anything new pops up and post results when I replace the PCV.



      • #4
        Just to update on this fault, I replaced the purge control valve and it instantly solved the problem, been driving around now for about a month and no issues - thanks


        • #5
          Glad its sorted. Thanks for the update. It will help others.