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  1. #1
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    Idle + Throttle Blip = Engine Stall?

    Hey guys,

    I need a little help in diagnosing this issue. It's been ongoing since the start of winter. I thoguht it was fuel related, so I took a couple logs and replicated the issue, but it doesnt seem to be the case.

    If I'm just idling at a light, and blip the throttle to 900-1100 RPM, the engine will either: 1) drop RPM for a second to <400-500 RPM and bog or; 2) Stall entirely. I've also been having long (>3 sec) cranks.

    Maintenance done since noticing:

    1) I thought it was old NGKs, so I replaced those and the issue persists.
    2) HPFP replaced 60k km ago. Seems to meet target pressure at idle though.
    3) LPFP holds pressure at 72 PSI.
    4) Injectors replaced 20k km ago. Doesn't seem to be leak related, since AFR during coastdown (infinate AFR) is consistant. Also ultrasonic cleaned the tips, no change.

    There is a huge STFT swing after the throttle blip. Is the engine going pig rich and bogging? Any ideas are appreciated.

    In the following log, you can see RPMs recover and the engine did not stall:

    http://datazap.me/u/tzu/idle-revv-an...16-17-18-19-20

  2. #2
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    $#@!, just found a crack in my valvecover. Sucks because I just did VCG a month or so ago.

  3. #3
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    Click here to enlarge Originally Posted by Tzu Click here to enlarge
    $#@!, just found a crack in my valvecover. Sucks because I just did VCG a month or so ago.
    Just add more fuel, should work perfectly Click here to enlarge

    edit* joke, it was a joke, be easy.




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    My sympathies. Figuring out what caused the valve cover to crack is the question now. If you could post a pic, I would very much appreciate it, very curious as to what insufficient bov, recirc related failures manifest themselves as.

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    I have the exact same issue. I posted a video awhile ago. I can get the car to stall out with a throttle blip at idle. How did you find the crack? I replaced all the vacuum lines but never found a definite leak.

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    I have no idea what is causing this bog. I'm hoping someone else who has logged their startup and idle can comment on the HPFP fuel pressure. Might just be as simple as a bad HPFP.

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    Click here to enlarge Originally Posted by BoostinBiscayne Click here to enlarge
    My sympathies. Figuring out what caused the valve cover to crack is the question now. If you could post a pic, I would very much appreciate it, very curious as to what insufficient bov, recirc related failures manifest themselves as.
    The plasic valvecover gets brittle over time. When it's torqued from factory, and subjected to thousands of heat cycles, it settles into a very slightly different form. If you don't torque it to it's exact position when changing the VCG, you're loading it ever so slightly differently than before, with heat, and it'll stress appropriately. My VC looked like it was in good shape so I replaced gasket only. Word to everyone here, just buy a new valvecover to begin with.

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    Try resetting fuel adaptations.

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    1 out of 1 members liked this post. Reputation: Yes | No
    Tzu,

    I also suffered from a cracked valve cover. Fortunately, it was covered under warranty at about 43,000 miles. As far as I know, (I have all service records as it is a CPO) the valve cover had never been removed prior to that point since new. Idle quality was poor, very much like a vacuum leak. The more I look around, the more common a cracked valve cover appear to be.

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    Click here to enlarge Originally Posted by eric84405 Click here to enlarge
    Tzu,

    I also suffered from a cracked valve cover. Fortunately, it was covered under warranty at about 43,000 miles. As far as I know, (I have all service records as it is a CPO) the valve cover had never been removed prior to that point since new. Idle quality was poor, very much like a vacuum leak. The more I look around, the more common a cracked valve cover appear to be.
    Where was it cracked? Where should I be looking for a crack?

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    Click here to enlarge Originally Posted by stangorang Click here to enlarge
    Where was it cracked? Where should I be looking for a crack?
    I wish I knew. I asked the Service Advisor and he did not know. He acted like it was pretty rare but the more I read, the more common it appears. I can tell you my rpm on the tach would vary noticeably if that helps.

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    Cracks can appear anywhere, especially if you like to lean on the VC. I'm going to replace the VC entirely and report back. PCV issues can usually be a primary contributor to idle issues.

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    Here is what my car does with a little throttle blip from idle.


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    My idle wont oscillate, the engine will just bog once or die.

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    Click here to enlarge Originally Posted by Tzu Click here to enlarge
    Cracks can appear anywhere, especially if you like to lean on the VC. I'm going to replace the VC entirely and report back. PCV issues can usually be a primary contributor to idle issues.
    yeah......Ivo warned me about this. People don't realize that the valve cover is a very thin plastic material and when we inspect or work on our engines we all tend to lean on it without realizing the stress it is putting on it.

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    1 out of 1 members liked this post. Reputation: Yes | No
    Click here to enlarge Originally Posted by stangorang Click here to enlarge
    I have the exact same issue. I posted a video awhile ago. I can get the car to stall out with a throttle blip at idle. How did you find the crack? I replaced all the vacuum lines but never found a definite leak.
    Issue has been reduced 80% by replacing the leaking PCV system. Still a bit of a bog, but isn't as inclined to stall anymore.

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