Subaru 2004 2l auto tip tronic. It seems to hesitate or have slow or lack of power when you accelerate slowly
What you need for proper engine operation is a) air, b) fuel & c) ignition. If the the air intake is not obstructed, the throttle plate/cable not loose or sticking, then look for spark plugs and ignition wires. If all that is sorted out, look for fuel pump issues, or sensor errors (although you did not mention a check engine light).
Most likely you need to replace the plugs, and/or the ignition wires.