BMW Repair: 87 bmw 325is, air flow meter, bmw 325is

Question
When I turn on my car, the rpm goes up and down when it's in neutral, but when I'm on the road driving, it works fine. First they said it was the air flow meter, so I changed it, but it's still doin' it. I also changed the idle control sensor...and it's still doin' it! Also, I checked for vacuum leaks and found none, yes it is still doin' it. Can you please help me locate the problem to keep it from doin' it.

Answer
Carlos,
 I would have told you to replace the air flow meter, idle control valve, and everything else you did.  You can check on the thermostat housing, there are a few sensors.  One tells the computer when the car is up to temp, and it will idle the engine down.  This sensor goes bad and causes problems like this.  Check this sensor.

 Good luck,
 Josh