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Thread: engine "bouncing" under throttle at low to medium revs

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    engine "bouncing" under throttle at low to medium revs

    My sons N15 Pulsar has a GA15DE engine, from what i have seen they are pretty much the same engine as the GA16DE so i will post this here in the hope of some help. Sorry if it is the wrong spot.

    The car is a manual with about 150km on it which we recently bought to teach him to drive in and for the most part runs fine, it accelerates fine and maintains speed fine. However it does a kind of throb or bounce (sorry, cant think of how else to describe it ) when under constant throttle at low to medium revs, either cruising at a constant speed or accelerating. At high revs it is fine, though that could just be the momentum of the engine smoothing things out.

    It also sometimes feels like it bunnyhops in 1st gear fairly easily, but that could just be me becoming reacquainted with a smaller engine manual car again (and him abusing the clutch :P ).

    I have given the car a good service since we got it which has helped; oil & filter, plugs, fuel filter. Also had to change the CV joint and thermostat, but i doubt they will be related. I was thinking about perhaps trying to clean the MAF, but this one is a little different to the others i have worked on, looks like its embedded in the throttle body. Not too sure how to get at this one, not sure if there is a how to section for that?

    Engine mounts seem ok, the engine isn't moving around on them when getting on and off the clutch at a standstill, though i guess that doesn't mean much.

    Does anyone have any other thoughts what to try?

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    bump?

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    Need Input Cozzm0's Avatar
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    The MAF is usually attached to the Airbox with a separate Intake Temp Sensor on the GA series motors i believe, but we don't have the GA15 in Australia, only GA16. Sometimes the single wire Oxygen sensor used on the GA goes bad as they rely on the exhaust temp to heat them up (instead of the 3 wire heated version used on the SR). This might also be giving 'bad feedback' to the ECU and causing hesitations.

    Make sure anything you use on the MAF is designed for it, using harsh cleaners like throttle body cleaner can damage the air flow sensors.

    Might be worth checking for cracks/leaks in intake pipe too as any kind of vacuum leak can make the car run quite lean which makes it feel like its being held back.

    Disconnecting the battery and reconnecting it after a short time (couple of minutes) can also reset the ECU self learning / fuel trim which if the O2 sensor is bad, even if replaced, will maintain some of the hesitation feeling if the fuel trim isn't cleared out (with laptop connection or by disconnecting battery).

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