$4,000 · 2003 subaru impreza 2.5RS

2003 Subaru Impreza 2.5RS 5 speed manual. Car has had lots of money put into it by me. New LUK clutch kit, New Felpro Head gaskets, new valve cover gasket kit, gates timing belt kit about 5000 km ago, wrx suspension, new coil pack, new plug wires, new spark plugs, head have been machined before new HG new front and rear o2 sensors, new cat converter, new custom catback exhaust, new neutral switch,new rear main seal, New throttle position sensor and probly forgetting about a few things. Car idles perfectly fine, but when driving it bucks and acts like the throttle was let go, rpms drop like u let go of throttle, no response till u play with pedal a bit. No codes being tossed, ive tried o2 sensors neutral switch, new fuel injectors new idle air control valve and still not fixed. I am stumpped on this issue. might be the engine bay harness. I bought a spare good harness but my job give me hardly any free time to do the swap. heads valve covers and manifold were painted. Car comes with spare 5 speed transmission spare wiring harness, spare ecu, 3 spare idle air control valves that all work, spare driveshaft, spare throttle position sensor and a few other parts like water pump and timing belt tensioners. lots of spare parts to go with car. Im well over 6000 into this car. asking 4000.