Hyundai Ix35 P0638 Code: Engine Light On, Acceleration Issue After Key Start

My Hyundai Ix35 has been displaying a check engine light and the fault code P0638. The car fails to accelerate properly when starting with a standard key turn (no hold or pause), but if I insert the key and immediately start the engine without holding it, the vehicle accelerates normally. This intermittent behavior is concerning. I suspect an issue related to throttle control systems. Possible causes include: pedal position sensor malfunction, throttle position sensor failure, throttle actuator motor issues, dirty throttle body, wiring harness faults, loose or corroded connections, or a PCM/ECM malfunction. Can anyone confirm if this P0638 code is commonly linked to such acceleration problems in Hyundai Ix35 models? Any diagnostic tips or testing procedures would be greatly appreciated.