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My car is a Toyota MK4 NA Supra and it has a problem I don't understand. When I push the throttle gently, whether in park or in drive, it gradually builds revs and moves but when I push it hard i.e flat out, it acts like it's misfiring/backfiring and doesn't move. I have to feather it ever so gently. It's way worse in the mornings when it's cold. Please I need all the help I can get.

Is it my spark plugs?

leaking vacuum? etc

Thank you guys!

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  • Any codes or recent changes?
    – rpmerf
    Feb 25, 2016 at 16:36
  • No. ECU doesn't give out any codes unfortunately. Feb 26, 2016 at 17:28
  • Thank you everyone. It was a blocked fuel filter all these while. I feel a little stupid. Thanks for your amazing help. All fixed now. Mar 14, 2016 at 19:31

2 Answers 2

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Hard to say with the information given. Sounds like retarted timing or not enough air or fuel (too rich / lean) . A repair manual will be infinitely useful in testing/troubleshooting.

Things to test:

  • codes, even if the CEL isn't on there might be something stored.
  • air filter
  • spark plugs (clean, gapped correctly)
  • wires
  • cap
  • rotor
  • coil
  • vacuum lines (check engine vacuum)
  • fuel filter
  • fuel pump (check fuel pressure)
  • sensors - MAF, MAP, o2, cam/crank would be most likely to cause these issues. Should be able to read with a multimeter.
  • Idle motor - stuck open can be similar to a vacuum leak
  • knock sensor, it might be causing the ECU to pull timing
  • timing (timing light, base timing, determine if ECU is pulling timing)
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  • Thank you for this list I'll check a few tomorrow and get back to you. Thank you. By The Way, when I Put my foot down, it sounds like it's backfiring like there's air packets in the system somewhere and the airpackets are bursting. I dunno how to explain that sound. sigh Feb 26, 2016 at 17:22
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    @NwankwoOnyedikachim It's gonna come down to fueling, timing or a plugged cat more than likely. I'd check engine vacuum first as it's the easiest to do and will generally indicate where you should go from there.
    – Ben
    Feb 26, 2016 at 21:04
  • Good call on the clogged cat.
    – rpmerf
    Feb 26, 2016 at 21:21
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I had a similar issue with one of my cars, after poking and prodding it for a couple of days it came down to the butterfly valve in the air intake sticking, if you throw your foot flat to the floor and it can't suck the air in quick enough it won't have the right air to fuel ratio and run awfully.

Just remove your air intake and get someone to rev it slightly and make sure the valve is opening and closing easily (Don't do it too much without a filter on or you'll end up sucking in dust and other engine related things)

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  • The butterfly valve is directly tied to the throttle only on older cars, why would the air-fuel ratio be wrong if the throttle sticks? Feb 26, 2016 at 10:40
  • because the more you put the accelerator down the more fuel is thrown into the engine, the more air is needed for oxidation(combustion) Feb 26, 2016 at 10:49
  • No, the more you put the accelerator down, the more air is thrown into the engine, and the amount of fuel injected is calculated accordingly. Feb 26, 2016 at 12:31
  • I'll try this tomorrow morning and report back. Thank you. Feb 26, 2016 at 17:23

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