BMW Repair: Misfiring and EML light, mass airflow sensor, bmw e46

Question
I have a BMW E46 328I Saloon. Basically the car starts fine and drives all okay for around for around 5 minutes then when the revs go to around 3500 plus the EML light and ASC light and a light that looks like a cog with an exlaimation mark appears !! The car then missfires and cuts out !! The spark plugs, fuel filter, Air filter, mass airflow sensor have all been changed and the problem is still there !! Any Ideas will be most greatful ! P.s. Put in on 3 different diagnostic equiptement and they all report different faults I think it's something minor but hey who knows ?

I get a fault code of potentiometer pwg 2 - if this has failed how to I replce it - is it easy ?

Thanks again  

Answer
John, PWG 2 is the potentiometer in the throttle assembly. Please swap in a new throttle body (under the intake manifold below the idle valve.) Remove the idle valve and clean it while you are in the area. You should hear the idle door move if you twist the valve rapidly with your wrist. Replace any torn/cracked intake boots you find. and clear faults. With the new throttle in the car turn the key on for 15 sec. and then off for 15 sec. Then you can start the engine and test drive.
-Evan