You need to get your car hooked up to a computer that can check for faults in that area. Either the dealer, or an independent shop that has something like an Autologic scan tool is necessary. There is no sense throwing parts at these cars until you do this; many new components will not even work until coded by the scan tool. Not to mention that the scan tool can often point you to the exact location of the problem.

__________________
2014 BMW 328i Xdrive
2011 BMW 335i M-Sport
2008 BMW X5 4.8i Sport
2000 BMW 528i 5sp