Q: Car stalling when I shift into drive.

Hello, Unfortunately a catalytic converter and oxygen sensor won’t cause a stalling concern when placed in gear. The first thing that should be done is have the car checked for codes. Check if the idle speed feel right and if not, the idle air control valve may not be working. Check the intake system for air leaks because an unmetered air leak will cause a lean condition. There could be an electrical fault or the torque converter is locked up. You may need the aid of a mechanic, such as one from YourMechanic, who can check for code and monitor actual values to see there is an indicator to the cause.