Q: how do i know if i have an bad PCM

PCM’s are usually replaced at the end of a "process of elimination". That is, with most engine management control failures, there are a whole host of common causes that are evaluated first. Once that long list of most common causes is exhausted, at that late stage (or as a final step) PCM substitution would be considered. I can all but guarantee that you do not have a failed PCM though because such failures are so rare. Indeed, statistics show that of the PCM’s returned for warranty claims, half of those returns are in fact perfectly good (no failure)!

Common causes of engine stalling and rough idle include a faulty mass airflow sensor, faulty engine coolant temperature switch/sensor (typically at cold start only), worn spark plugs, wires or defective ignition coil(s), inadequate fuel delivery or pressure (clogged fuel filter, injectors), contaminated or old gasoline, defective throttle position sensor, faulty idle air control valve, leaks in the EGR system, intake vacuum leaks, and so forth. If you request an engine stalling/rough idle diagnostic the responding certified mechanic will get this resolved for you promptly. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.