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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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    Quote Originally Posted by Cozzm0 View Post
    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).
    The GA15DE has the MAF inside the throttle body, its a weird setup from my perspective compared with others. Makes it a PITA to get to and clean as you apparently need to remove it from the car, cut the silicon and pry open the cover and remove the circuit boards . Its off a JDM imported Pulsar, there are loads of them over in NZ now. I have the proper MAF cleaner so no worries there. I might just have to get another from the wreckers and see if that fixes it, was hoping not to have to.
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    The battery has been replaced recently so the ECU should be reset from that process. Seeing as the throttle body has the MAF inside it i had pretty much ruled out a vaccuum leal, but now that you mention it i suppose it is still a possibility maybe in the gasket or somewhere. will check it out.

    Thanks for the help, if you guys have any other ideas please keep it coming.

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    Need Input Cozzm0's Avatar
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    wow that's an ugly setup.. lol

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    Quote Originally Posted by Cozzm0 View Post
    wow that's an ugly setup.. lol
    lol, you are telling me!

    I must be a glutton for punishment as i have gotten both my kids an N15 with the same setup, just 1 auto and 1 manual. They are pretty simple and robust cars though, and have been great 1st cars so I cant complaint too much.

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