Rough idle, jerky acceleration and occasional stall. Need help to analyze fuel trims.
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Thread: Rough idle, jerky acceleration and occasional stall. Need help to analyze fuel trims.

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    Rough idle, jerky acceleration and occasional stall. Need help to analyze fuel trims.

    Hi all, Iím new to this forum - my car is Cayman S í14 PDK. I love the car but now it has become more and more jerky especially at low revs.
    It has also slightly uneven idle (+-50rpm) and occasional stalling. At high revs the power seems to be ok.

    What I have done so far:
    - new spark plugs with coils
    - new lambdas
    - air filters
    - cleaned throttle valve

    After doing those the problems still persist. I purchased diagnostic scanner to read the codes but there are none.
    However the fuel trim values are a bit weird:

    B1 LTFT B2 LTFT
    Idle: +1%. -1%
    1500rpm 0%. -9%
    2500rpm 0%. -8%

    The STFT values are ok and within +-3% almost all the time.
    Does anybody have any idea how to interpret the LTFT values?
    Why would my trim values become more negative along with the revs and only for one bank?

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    Re: Rough idle, jerky acceleration and occasional stall. Need help to analyze fuel tr

    I donít have an answer for you bud, Iím just bumping your thread. Youíve done everything that I would have done.

    I understand that uneven acceleration goes away with high-flow cats so Iím wondering if it is exhaust sensor related.

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    Re: Rough idle, jerky acceleration and occasional stall. Need help to analyze fuel tr

    I copied this brief explanation that explains Fuel trims

    Short term fuel trim adjustments are short temporary adjustments that happen immediately. Long term fuel trim is accumulated over time and stored in memory. It is often the result of several STFT adjustments that exceeded a 25% increase or decrease over time.

    Basically the closer to zero you get the better it is. The long term trims go up if there is a permanent adjustment needed to compensate for a malfunction some where or just because some of the emissions sensors are deteriorating like a dirty MAF for example. Long term trims at 20% usually indicates something is wrong some where cause a big adjustment to the Fuel/air ratio.
    2014 Base Cayman, M/T, Rodium Silver, Agate Grey/Amber Orange interior, Sport Wheel, Power Folding Mirrors, Bose Infotainment...

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