01' 325i rough idle
 

I've had my car for two years and basically had this problem the whole time. The guy who owned the car before me took it in to bmw for the same issue. The car idles rough, especially in cold weather. It isn't really bad, the way a misfire would rough idle, but its noticeable. When I put the transmission in neutral the rough idle goes away and runs as smooth as if the car were off. But in drive and at a stop, it feels like you're driving over a gravel road. I also took it in to bmw to have them check it out. They basically told me it was normal, but that I might want to consider getting a fuel injector flush service. Theses are the same guys that told me it was normal to hear a high pitch whistle at high rpm and couldn't find anything wrong with the car. After I got home it took me all of 30 seconds to find a finger size hole in the back of my throttle intake boot. After replacing the boot MYSELF, the high pitch whistle went away and the rough idle seemed to stop as well. However, recently the car seems to be idling rougher and rougher, but I can't find anything wrong. I still get a high pitch whistle at about 6000 rpms, but it isn't nearly as audible as when my intake boot was cracked. I'm suspecting another vacuum leak somewhere, or possibly a faulty idle control valve. I have no idea where to start looking though. I have no abnormal fault codes either. Anyone had similar issues or know of a good place to start troubleshooting?

I'm guessing that the car is an auto and has 120k+ miles if it is I've seen this issue before in alot of cars I really haven't got a good answer as to why though all I can figure is that it has to do with the converter grapping a little as for the wistle its in the intake some where I would just look it over closely and look at the conections and where anything might be rubbing

It is an auto, but only about 92k miles. Is there a way to troubleshoot the converter without replacing it?

I'm not even sure if it is the converter but I would have to say talk to your local transmission shop a place that only dose transmisions that way your talking to guys that are really good at it and they should point you in the right direction and hopefully its a cheap fix mabey even just a flush and filter change and check you fluid level mabey your just low

I am not sure if your model has it, but it is a common problem, under the intake manifold, behind the throttle body, there is a vacuum PCV valve, and commonly these things screw up and cause a rough idle, usually some fuel trim codes as well as others,the valve as well as all the hoses must be replaced, and some of the northern climate cars have a heater involved as well!!.