My '99 escort 2.0 SOHC has a jerking and sluggish response at part throttle. If I step on the gas to pass someone it responds fine. It seems to only happen after third gear while my foot is slightly on the pedal. I took it in to have the fuel filter replaced with no improvement and found out that it has a P1506 code for an Idle Air Control valve. Could this cause the problem at part throttle?