BMW: Idling problem, air flow meter, bmw 325e

Question
Hi Josh,
I've got a 1985 bmw 325E I just purchased really cheap, The car seems to have a lot of issues. My main concern at this time is in neutral the car idles at 3000 rpms. I replaced the alternator today, and put in a k&n filter I drove it around the block twice and it was trying to idle at 4000 what could possibly be the problem, and thank you for any suggestions. I'm not much of a mechanic, and am on a somewhat limited budget. Happy Thanksgiving

Answer
Daryl,
 Unfortunately there isn't a simple "here's how to fix it" answer for this.  It sounds to me that you have a vaccum leak somewhere and the engine is breathing in un-metered air.  This seems to be an extreme case, but I guess its possible.  Also when the car is in gear, does it try to rev up to 4000rpm as well?  Obviously you would have your foot on the brake, but is it pulling like you are putting your foot on the gas?

 The problem could also be electrical with it being the Air flow meter, or the Idle Control Valve.

 Check these out and see if it helps,
 Good luck,
 Josh