Q: Kia Optima hesitates when in gear. Does not while in park. It has slowly became worse over the course of many months. It still dr

If the transmission is not faulty (e.g., clutches slipping) and thus the problem is engine related, among the possible causes of the hesitation are faults in the throttle position sensor, mass airflow sensor, vacuum leaks, a clogged fuel filter, defective EGR valve or control circuit, and worn out spark plugs and wires. A mechanic would simply investigate these possibilities sequentially and also check to see if any diagnostic trouble codes can be downloaded from the PCM. If you want these steps performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request an engine hesitation diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.