Q: Hi! Thanks for wanting to help!! 2003 bmw 325i. (M54 - Automatic) Car ran really rough before I started work on it. Shaked/ran ve

Check for vacuum leaks, including that through a malfunctioning EGR system. When you first start the car, on cold start the mixture may be rich enough to overcome such leaks, but almost immediately the ECM can’t keep up with the unmetered air. Increasing engine speed diminishes the proportionate effect of the leak and that’s why you can run at speed but not at idle. Use a scan tool to test the throttle position sensor and further evaluate the idle air control valve.

Another possibility is the mass airflow sensor. Ideally if you’re trying to a diagnose a problem like this, use the OEM sensor. Non-OEM parts make a difficult diagnostic even worse as the parts don’t function based on the original engineering design. With regard to the mass airflow it’s not unheard of to have a 5 volt reference problem created by another failed sensor. If this is the case, you will need a scanner to watch the 5 volt reference while unplugging sensors one at a time. You will only need to unplug the sensors that use the 5 volt reference. A wiring diagram will be necessary to identify the correct ones. Another possibility is a jumped timing belt. This is easily checked by measuring compression of each cylinder. If the timing belt has jumped, at least one cylinder will be significantly lower than the others. Then check the cam timing to be sure. Check base ignition timing at idle.

YourMechanic offers a stalling diagnostic. If you request that service a certified Mechanic, dispatched by YourMechanic right to your location, will get this problem 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.