Q: my car would stall if I turn on the A/C while idling at a stop... sometimes it would run fine until the engine is not warm

Hello. Most of the time this is caused by a failing air flow sensor or an issue with the throttle body. The throttle body tends to get dirty which causes the throttle plate to not function properly, causing a low idle. If this occurs the computer cannot adjust the idle enough to keep the engine running. The idle control valve should also be tested to see if it is failing. If you plan on having this poor idling problem repaired, consider having a technician from YourMechanic come to your home or office to diagnose your stalling problems and replace the airflow sensor or throttle body if necessary.