BMW Repair Questions? Ask a Mechanic for Answers ASAP
idles rough...my daughter bought the car used and has had it for a few months before the service engine light came on. the previous owner had new battery put in and spark plugs changed.
PLEASE NOTE THAT I WILL NOT BE COMPENSATED WHATSOEVER UNTIL YOU PRESS THE ACCEPT BUTTON. NONE OF YOUR DEPOSIT WILL BE TRANSFERRED TO ME UNTIL YOU PRESS ACCEPT
Okay, the first thing to do is to clear all of the codes and see which come back. I doubt they all will if the check light just came on now.
Based on the codes present currently, the rough idle and common issues on this vehicle, I suspect the cause of the issue is an intake vauccum leak (unmetered air leak).
Unmetered air leaks allow excess air into the engine and cause the fuel/air mixture to go out of alignment and cause idle fluctuation like you are experiencing. They would also set the p0170, p0173 and misfire fault codes you have.
To check for vacuum 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.
Please let me know if you have further questions. If satisfied with my assistance, please press ACCEPT so that I am compensated for my time, effort and expertise. I am not compensated whatsoever until you press accept. None of the deposit you have paid will be transferred until you press ACCEPT.