I drive a Subaru Legacy Turbocharged GT 2008 model with an EJ20 engine.

When I press hard on the acceleration to boost the tachometer upon reaching 4-5 thousand RPM's it starts jerking and there is no acceleration. However, if I accelerate slowly I don't experience any issue at all. The fuel filter and pump were checked and are OK, so are the plugs. An engine diagnosis was done and revealed nothing.

What could be the issue?

  • 2
    You should check the live fuel trims to see whether the engine is starving of air or fuel for starters, there are many reasons why this could happen. Commented Jan 14, 2016 at 8:27
  • 1
    Are all the hoses connected to the turbo and waste gate? Do you have a boost gauge? Is it reaching boost?
    – Bob Cross
    Commented Jan 14, 2016 at 13:16
  • Check the oil. Does it smell burned?
    – race fever
    Commented Jan 14, 2016 at 14:38
  • Is it modified? Do you have access to an AccessPort or some other device that you can plug into the OBDII port to log the parameters your ECU is utilizing?
    – Ellesedil
    Commented Jan 14, 2016 at 22:50

1 Answer 1


Sounds like an Air Passage issue to me. This could mean: a bad Mas Air Flow Sensor or maybe a poor Throttle Body Sensor, and maybe even a clogged EGR Valve or a dirty Throttle body Unit. These items can clog with carbon and need to be cleaned or replaced after time. These items cah each be checked with a Probe Light Tester first to make sure you're getting power to each item. Try to think in terms of a gas cooking stove-- there are tubes inside that lead to each particular burner to control air flow, these tubes have adjustable windows for air flow. If the air tube is opened too much or closed too much you will not get proper flame to your stove top it will ignite and blow itself out or it will spew gas and not ignite at all, or the flame does not come through as a healthy flame.

  • When you say "probe light tester" I'm thinking your referring to a test light where you ground the aligator clip and poke into wires to see if the device lights up when it get's power through the probing. Commented Jan 18, 2016 at 0:12

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