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Thread: my car RPM drops significantly when braking with clutch pressed

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    nauman.hanif.9's Avatar
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    Default my car RPM drops significantly when braking with clutch pressed

    i have 98 civic with dual vtec D15B, the rpm remains stable and gives no problem when the car is idling.
    while cruising, as i apply brake with clutch paddle pressed, the rpm drops signifcntly in petrol and the problem is more sever in cng. the rpm drops to zero and i have to start my car again or shift down to a lower gear and then release the clutch and the engine would start again.
    i cant use the CNG anywhere in local, just on motorway and that too as far as i dont use the brake.
    the assembly is new, spark plugs are new, throttle body is cleaned, air filter is new. tuned my car a hundred times in cng but it doesnt solve the problem at all...................

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    ZainMahdi's Avatar
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    Default

    If the rpm drops very suddenly before the engine stops, it could be a worn out dashpot. The dashpot slows down the throttle closing when the driver lets off the pedal, so the rpm drop is slightly slower. This prevents a sudden rich condition for the engine, starving it of air and causing it to shut off.
    The dashpot is supposed to be connected to the throttle body.

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    Default

    where is this Dashpot and what is the name commonly used for this thing?

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    Default

    what is dashpot?

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    Default

    First of all isolate the problem,either it could be because of voltage drop or heavy vacuum leak.
    To check voltage drop disconnect the brake light by removing wires from brake light switch or fuse from fuse box,then apply brake and see the result,if there is no rpm drop,then check brake light wiring for bad connection and short circuit and as well as alternator's out put voltage at idle rpm.
    If problem remain persist then check the brake booster and its fittings.
    Never loose hope in life,every step gives u something.

  6. #6
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    the brake voltage drop has been checked, even if i have not applied brakes and just press the clutch pedal whille cruising, my RPM drops to zero........ it drops to 200-300 in petrol, and in CNG it drops to Zero

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    Default

    Have ur tappet adjusted when engine has been shut for more than 6 hrs vtec engines required to be dead cold for adjustment I had a similar problem and my tappets were tight remember it's very important that engine is cold like less than 38c hope that helpps

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