MY Kia Sportage 2009 has low power getting from idle

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MY Kia Sportage 2009 4WD has low power getting from idle I had to press the accelerator so hard to make it move from idle state. Also whenever I slowed down, to pick up momentum and move I had to pump on the accelerator but when it is on high speed it accelerate well. We had changed the fuel pump but the problem persist. The technician said he suspect leakage in the fuel pump casing.