Hi all, I have owned a 2006 Impreza for a year now and just can't get it running right. The issue is, when under acceleration it has a flat spot when under 3,500 rpm. It sputters and gurgles until it reaches 3,500 to 4000 rpm then takes off like it should. I have had it in various mechanical workshops and have spent over $2000 replacing all the sensors, fuel pump, spark plugs, throttle body cleans ( twice ) And I only run premium unleaded fuel. What am i missing ?? Please help !