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Thread: Engine stumbling

  1. #1
    Member
    Join Date:  Jul 2020

    Location:  Danvers, ma

    Posts:    53

    Engine stumbling

    Hey everyone, just a quick question. I am going to change my plugs and wires soon but I have some engine revving issue. From an idle, if I stop the pedal down and rev it up (in neutral) the engine stumbles until i gets up past 2000rpm or so then it spins up great after that. If I slowly push the pedal down and let the rpm's climb slowly then there is no hesitation. I'm pretty sure my car is running rich because I still cannot get it to go into closed loop. Frequency valve doesn't buzz. Only does this at low rpm while driving also, once I get above 2-2.5krpm the engine is smooth as can be. Thoughts?

  2. #2
    Under Ron's watchful eye. Glory be to Ron! Michael's Avatar
    Join Date:  May 2011

    Posts:    4,152

    My VIN:    A bunch of numbers and letters that should not interest you.

    If it happened all of a sudden, check your vacuum lines. Have you recently been under the hood prior to this?

  3. #3
    Member
    Join Date:  Jul 2020

    Location:  Danvers, ma

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    No it hasn't happened all of a sudden, it's been like this. I got to replace the original vacuum lines one of these days

  4. #4
    Member
    Join Date:  Jul 2020

    Location:  Danvers, ma

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    There's no disconnected lines, but i can't imagine a small bad seal could cause this kind of noticable engine preformance decrease/hesitation?

  5. #5
    Delorean Guru
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    "Stomping" on the throttle and noticing hesitation in neutral is not a real test of anything. Do the tune-up. Check and if necessary change the air filter. Find and fix any vacuum leaks. Verify that all of the vacuum hoses are routed correctly, everything works, and no leaks. Check all of the throttle adjustments. Do a compression test and adjust the valves if necessary. Finally, check the A/F mixture and if necessary adjust the mixture screw. Make sure you get into "Closed Loop".
    David Teitelbaum

  6. #6
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

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    My VIN:    03572

    A wrong set mixture could do that. Get a dwell meter and check or set your mixture.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  7. #7
    Senior Member
    Join Date:  Nov 2014

    Location:  Alexandria, VA

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    Also check your timing.

  8. #8
    Member
    Join Date:  Jul 2020

    Location:  Danvers, ma

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    Quote Originally Posted by Bitsyncmaster View Post
    A wrong set mixture could do that. Get a dwell meter and check or set your mixture.
    I can't check my mixture because the well just shows a set value because i can't get into closed loop

  9. #9
    Under Ron's watchful eye. Glory be to Ron! Michael's Avatar
    Join Date:  May 2011

    Posts:    4,152

    My VIN:    A bunch of numbers and letters that should not interest you.

    Quote Originally Posted by TheStoot View Post
    I can't check my mixture because the well just shows a set value because i can't get into closed loop
    Well there is a pretty big red flag. Fix that first. Test and diagnose your o2 circuit.

  10. #10
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

    Posts:    7,996

    My VIN:    03572

    Quote Originally Posted by TheStoot View Post
    I can't check my mixture because the well just shows a set value because i can't get into closed loop
    If it holds (45 deg) with a warmed up engine than probably your O2 sensor is disconnected or bad. Another possible problem (holds 52 deg.) is the wide open throttle switch is always on.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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