C5 2004 v6 engine revs with AC ON
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Thread: C5 2004 v6 engine revs with AC ON

  1. #1
    Tadpole
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    Default C5 2004 v6 engine revs with AC ON

    When aircon is on the engine over revs and hunts up and down .It apparently went to 5000rpm when some one else was driving when it first started.Have to hold hard on brake when stopped as it really wants to lurch forward and is uneven when driving and upsetting gear box.It returns to normal with aircon off.
    Does anybody have any idea what this maybe, a sensor or will it be computer related. We already have an issue with the comm unit but that has only affected the lights and indicators.
    Thanks in advance and what a great forum this is.
    Regards Peter

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  2. #2
    Tadpole
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    O Forum Phantom,
    why hast thou forsaken me ?
    dave_R16TS likes this.

  3. #3
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    Default Stumped the forum !!

    Quote Originally Posted by ipodz View Post
    O Forum Phantom,
    why hast thou forsaken me ?
    Hi Peter
    Well I am not the Forum Phantom as far as I know but your plaintiff cry struck a cord

    My thoughts are mixed. If the engine has an electronic throttle them I have no idea what could cause this. If it has a mechanical or seperate throttle 'lifter' activated by the a/c switching on, then it may have malfunctioned. More details on the setup would be necessary to speculate further. I have not actually looked at a V6 engine in a C5.
    jaahn

  4. #4
    Tadpole
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    Hi Jaahn
    Indeed it is an electronic throttle and behaves perfectly until the air con is activated either by the climate control or front window demisster. My thinking is that the engine management is getting confused by a failed sensor or perhaps a relay.
    Regards Peter

  5. #5
    Now go make me a sandwich Hotrodelectric's Avatar
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    Quote Originally Posted by ipodz View Post
    O Forum Phantom,
    why hast thou forsaken me ?
    I'm more the Token Yank than the Forum Phantom and what I know about the C5 could be poured into a thimble with room for cream, but how old is the battery and is it up to spec? Alternator doing it's job? Battery cable ends clean and tight?

    The problem I'm on about is any of those three faults can cause some serious wackyness on a newer car like yours. Before you go any deeper, check those three items. One more thing- check and make sure all engine connectors, especially around the A/C sensors and switches are fully home.
    The measure of your character isn't what you do when people are watching- it's what you do when they aren't watching.

  6. #6
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    Default Phantom Strikes again !! :)

    Quote Originally Posted by ipodz View Post
    Hi Jaahn
    Indeed it is an electronic throttle and behaves perfectly until the air con is activated either by the climate control or front window demisster. My thinking is that the engine management is getting confused by a failed sensor or perhaps a relay.
    Regards Peter
    Hi Peter
    I think the answer lies in a Lexia. You probably need to hook it up to one and actually see what the commands are and the sensor outputs etc !! Not having done this I cannot add anything more but there are some Lexias over your way I am sure !
    My only other suggestion is a reboot of the computers by disconnecting the battery and reconnecting. Silly but it can fix some transient body glitches. Switch everything off and windows up and doors shut before disconnecting. Some things will need to be reset as in the book after.
    cheers Jaahn

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