BMW Repair: 1999 323i Idle problem and miss-fire, oil filler cap, bmw diagnosis

Question
Evan,

I am great need of your advice.  About a week ago I was having some serious problems starting my car.  I would have to crank the car over several times in order to get it to stay running, then eventually I had to start giving it a little gas to keep it running.  First I blamed the cold weather, however it just got worse.

The car started to miss-fire or at least that's what it sounds like to me, it had absolutely no power at all, very poor acceleration, etc.  I took into my mechanic (NON BMW)and he said that 5 of 6 cylinders were miss-firing.  He suggested that we change the plugs first and the coils as well which we did, this made no difference.

I am not too experienced with newer cars but to me it sounds as if the timing is off.  I can get the car to run for about 3-5 seconds then the rpms drop down the car starts miss-firing once and a while and it wants to die.

I feel that there is a sensor somewhere that isn't letting the plugs and/or fuel system work properly.  My mechanic things that there is a problem with the computer.  The reason my mechanic feels this way is that the computer system locked out his "Genesis" Scanner from reading anymore after he was able to the first 7-8 times.

Sorry for the biography, I just wanted to give you as much info as possible.  Please let me know what you think, any insight on this is much appreciated.

Thanks again,

Josh

Answer
Josh, what fault codes did you get? What is the last seven digits of the VIN number? It doesn't hurt to take the car to the dealership to get a BMW diagnosis reports and copies of the fault codes to help your boy diagnose faults.
Please check the throttle hose where it connects to the idle valve for cracks and tears. Basically look for intake duct leaks. If the boot is torn replace it and remove the idle valve and clean or replace it. Also check the crankcase vent valve under the intake manifold by running the car at idle and just barely cracking open the oil filler cap. If you hear a odd noise then the valve is bad and should be replaced. These are just some common items that go bad on your model. How many miles?
-Evan