BMW Questions? Ask a BMW Repair Expert for Answers.
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Thank you for clarifying 1998.
It sounds very much like you have an intake air leak.
Unmetered air leaks allow excess air into the engine and cause the fuel/air mixture to go out of alignment and cause rough idle like you are experiencing. They would also set the fault codes you have.
To check for intake leaks, visually inspect the intake area for any cracked hoses/pipes. If you can't see anything, you can try this trick: spray a can of carb cleaner around the intake with the engine idling. If the idle changes, this indicates that the cleaner is entering the engine and you have localized the area of the leak. You can then inspect further.
Most common source of air leaks is from the rubber intake tubes between the airbox, and the throttle.
Another common issue that causes this problem is a failed crankcase vent valve. This is located under the intake, in front of the throttle body. This valve regulates a vacuum on the crankcase, when they fail, a high vacuum is put on the crankcase - giving an unmeterd air leak. You can check for this by removing the oil cap with the engine running, if the engine stalls, or idle dips a lot, and there is a high vacuum holding the oil cap down, then this valve has failed.
Aside from that, a bad mass airflow sensor or temp sensor could also cause what you are experiencing, but there would likely be other codes present if that was the case.
I hope that is helpful, please let me know if you have further questions, or if I can clarify anything for you.
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Most likely it is. Otherwise a proper diagnostic will need to be run to read the inputs and outputs from the temp and mass airflow sensor, and also the fuel pressure.
Thank you in advance.
Your crankcase vent valve will need to be replaced. Those noises are a tell tale sign of the ccv being faulty.