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Engine almost "stall" when change gear / release throttle in neutral

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  • Engine almost "stall" when change gear / release throttle in neutral

    When I drive my RS2 and change gear, during the release of throttle (gear in neutral) the engine rev drops around 500RPM and almost. It only happens whenever the car is warm up. Battery is just replaced but problem remains the same.

    I notice when this happens the voltmeter indicate the voltage has dropped a bit to less than 13V. Without this problem the voltage is usually slightly above 13V


    Could my problem be related to the alternator? If yes is 034903016NX the correct part no? can I use this no. instead 034903016 or any other cheaper approach to fix this issue?


    Here are the photos of what the voltmeter shows:
    RS2 >> Ferrari: Performance/look ratio

  • #2
    Not likely. The voltage probably drops because the engine revolutions (and hence also the alternator speed) have fallen below normal idle speed. Once warm, it may be the engine is supplied with slightly less fuel and ignition advance, as it assumes that correct idle should then be more easily achieved.

    Is your air cleaner stock and clean?

    It may be that you have an Idle Stabilization Valve (ISV) that may respond to internal cleaning. If yes, then try cleaning the ISV.

    Are you able to pull any diagnostic codes?

    See also Dave's post here:
    https://forums.quattroworld.com/s4s6/msgs/21853.phtml

    Comment


    • #3
      I had these symptoms when the idle switch in the throttle position sensor failed. It was ok cold but started failing as it heated up with the engine bay. You can test it with a continuity tester or ohmmeter between 2 of the output pins see Quattroworld FAQ.

      Comment


      • #4
        Originally posted by Lago Blue View Post
        Not likely. The voltage probably drops because the engine revolutions (and hence also the alternator speed) have fallen below normal idle speed. Once warm, it may be the engine is supplied with slightly less fuel and ignition advance, as it assumes that correct idle should then be more easily achieved.

        Is your air cleaner stock and clean?

        It may be that you have an Idle Stabilization Valve (ISV) that may respond to internal cleaning. If yes, then try cleaning the ISV.

        Are you able to pull any diagnostic codes?

        See also Dave's post here:
        https://forums.quattroworld.com/s4s6/msgs/21853.phtml
        Thanks for your input. I always suspect N71 is leaking but I've been told that the N71 has been replaced not long ago... anyway may as well keep one as spare first. I havent got the time to work on the car, but will try to check if there is any codes comes up with VCDS.
        RS2 >> Ferrari: Performance/look ratio

        Comment


        • #5
          Originally posted by Thecrispynoodle View Post
          I had these symptoms when the idle switch in the throttle position sensor failed. It was ok cold but started failing as it heated up with the engine bay. You can test it with a continuity tester or ohmmeter between 2 of the output pins see Quattroworld FAQ.
          Thanks for your input, yes this is also one thing that really could lead to this problem! I will take some time to do the investigation soon and keep you guys post.
          RS2 >> Ferrari: Performance/look ratio

          Comment


          • #6
            Originally posted by Lago Blue View Post
            Not likely. The voltage probably drops because the engine revolutions (and hence also the alternator speed) have fallen below normal idle speed. Once warm, it may be the engine is supplied with slightly less fuel and ignition advance, as it assumes that correct idle should then be more easily achieved.

            Is your air cleaner stock and clean?

            It may be that you have an Idle Stabilization Valve (ISV) that may respond to internal cleaning. If yes, then try cleaning the ISV.

            Are you able to pull any diagnostic codes?

            See also Dave's post here:
            https://forums.quattroworld.com/s4s6/msgs/21853.phtml
            I managed to drive the car today as well as doing the readout from vcds.

            looks like I'm running rich, the maf was replaced 3yrs ago. Not sure N75 was replaced or not. I did the boost leak test some time ago and I can hear the leaking noise around the N71.. perhaps I may as well replace the N71 first and see how it goes.
            Last edited by pcfnet; 17th September 2019, 08:19.
            RS2 >> Ferrari: Performance/look ratio

            Comment


            • #7
              Hi PCF,

              First let me say I have no experience on your type car, however if you can hear a leak during the boost leak check(?), perhaps you also have a vacuum leak at idle?

              Cleaning the ISV and/or repairing a possible vacuum leak first, may obviate any need to replace the N71, it may be otherwise fine.

              More about 00561, possible effect of vacuum leak on fuel pressure at idle:

              https://www.s2forum.com/forum/techni...nd-bad-on-fuel

              If you haven't, perhaps also try clearing the codes and then see what returns.

              Hth.


              Comment

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