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Car hesitate to move off

This is a discussion on Car hesitate to move off within the Mercedes-Benz CLA45 AMG forums, part of the Mercedes-Benz CLA Model Specific Forums category; Hi, I have a 14’ CLA45. Had the car for almost a year and no issue till last month... When stopping at traffic light or ...

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    Car hesitate to move off

    Hi, I have a 14’ CLA45. Had the car for almost a year and no issue till last month...
    When stopping at traffic light or idling randomly the car vacuum(I had a boost gauge) and rpm will go up and down and afterwards when I move off the car will hesitate to move but it’s only at 1-2k rpm and after that it will be fine. I have no problems at high rpm and even high speed drives. As this happens randomly at anytime of the day I had use xentry to monitor, there was no checklight Nor any fault when the issue happen. So if anyone could help me out here?
    I have replaced the MAP sensor, boost sensor and airflow sensor and also the pcv hoses (3 of them) from the black intake pipe from turbo intake area.

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    jmc
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    From nominal was it vacuum dips or vacuum spikes? Especially considering your obvious change of potential problem lines
    Just for kicks consider a smoke based leak test?

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    I would say spikes... done leak test all appears to be fine

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    For reference dips are lower vacuum and spikes are higher vacuum (in my terminology anyway)
    If there are no (obvious) leaks perhaps the spikes are due to a faulty sensor somewhere? Especially since its at the low load / low rpm end

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    Yeah most probably is some sensor somewhere but when it happens no fault on xentry.. just got an error today not sure was it due to the problem or not but it’s a pressure sensor in evaporative emission control system... found out that if the purge valve is faulty it might cuz the same exact problem

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    Gee something is choking the system ... hope you track it down and may it be a simple part swap

    Xentry logs dont necessarily flag issues down unless its a blatant violation of some rule eg charging system data runs do not warn of a dying battery not accepting charge cycles properly but a trained eye is needed to review the (somewhat long and complex) data plots to reveal abnormal trends etc ... but then not everyone is gonna hook up a multiplexer+laptop every time they drive

    That being said ... perhaps theres a data trail for the sensors in the purge path (during a bad/good condition drive cycle) and maybe any out of band data may point to a dying sensor? Just a thought ...

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    Replaced the part but it’s still the same..
    Any more ideas?

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    Geee starting to look like a wabbit hole ...
    If you are certain there are no hose or coupling leaks (external) then one thought is to look “inside” with a compression test ... an act of congress somewhat ... and not the usual dealer response of “within spec” but the overall variance between the cylinders
    Speaking of (external) leaks ... did the smoke act funny hear the intake gasket and throttle body?

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    All is good for the smoke test.. still having problems yet no checklight... even use xentry to check but there isn’t any checklight

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    How about more basic data like misfire counts? Cat temp?

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