Answer

Thanks, the first step is to pull a code from the engine computer and see what relation it has with this problem. Sounds like you may have a typical MAF (Mass Airflow Sensor) failure.

Use the procedure below to get codes watching the check engine lamp flash, it's difficult to enter the manual self-diagnostics on these so you may need to do it a few times. Let me know the codes and we'll determine what's going on.

With Flash Codes Notes

NOTE : All troubleshooting should begin by "Checking the Basics" . Certain basic faults can be undetectable by the self-diagnostic system of the DME control unit and in some cases can actually interfere with the self-checking and fault memory operation. Refer to "Checking the Basics" . See: Initial Inspection and Diagnostic Overview\Initial Inspection\Checking the Basics In the event of a DME system malfunction, circuit information will be stored in the internal memory of the DME control unit. Intermittent failures are stored with a record of the failure frequency. The DME control unit is able to store up to five malfunctions, and will give priority to those items which can cause the vehicle to exceed exhaust emission standards. In addition to being stored in memory, an emissions-related failure will cause the "Check Engine" light to illuminate on the instrument cluster. Furthermore, the "Check Engine" light is used to display faults which are stored in the control unit's memory when the self-diagnostic procedure is initiated. Faults may also be retrieved with the BMW service tester if available. Entering Self-Diagnostics Switch the ignition to the run (ON) position. Depress the accelerator pedal five (5) times to the wide open throttle position within five (5) seconds to display flash codes for DME control unit 1. The accelerator pedal must be depressed six (6) times to display the flash codes for DME control unit 2. NOTE: Since the BMW V12 engine uses two independent DME control units, fault codes and procedures must be followed for the specific system. DME system 1 fault codes affect cylinders 1-6. DME system 2 fault codes affect cylinders 7-12. Read and record any flash codes that are displayed. Refer to the "FAULT CODE CHART" for the affected component or system. See: Diagnostic Trouble Code Descriptions Continue with the diagnosis procedures as outlined in "FAULT CODE DIAGNOSIS" . See: Reading Diagnostic Trouble Codes Repair or replace the affected component or system. Clear the fault code. See: Clearing Diagnostic Trouble Codes NOTE: To achieve good mid-range torque characteristics, long air intake pipes are used. This method of induction requires that the plenum chamber for the left bank (cylinders 7-12) be mounted on the right side of the engine, and the plenum for the right bank (cylinders 1-6) be mounted on the left side of the engine. The technician must keep this in mind when referring to component locations and testing procedures. Components such as air intake sensors, air mass sensors, injectors, throttle position motors and induction systems may be misdiagnosed because of the possible confusion. Remember that fault codes will always refer to the DME system (DME system 1 = cyl. 1-6) and (DME system 2 = cyl. 7-12).