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?
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.
