I started having a problem with my Z4, the symptoms was on long fast runs at high revs when backing off i would occasionally get the engine management light on. This would throw up lean mix code in both banks 1 & 2. I would use carly to clear and and it would stay off for a month or two.
However before Christmas one day the car started up and struggled to idle, even in neutral the car when pressing the accelerator it would struggle to keep the revs, the car was responding if the throttle fly by wire system was not working properly, so i inspected the inlet hose and before people say check the inlet boot by the idle for a spilt, my M54 3.0i is different as its supercharged!! therefore the pipes are different.
Cut a long story short i replaces the MAF, ICV, DISA valve, oil breather hoses each side of the CCV, the oil ring on the dipstick, change spark plugs and coil packs. Took all hose off supercharger and check and refitted.
I then check car via DIS v57 and eventually no lean codes as i had a leak on the DISA O ring which i then replaced again, car still not idling!! so off with the ICV and throttle body to inspect, replaced accelerator pedal as this has a sensor in!. Whilst Throttle body was off i sanded down the inside to remove the lip either side of the valve. replaced ICV again this time with a Bosch part but still not joy.
Finally sorted the issue which was the aftermarket MAF units (2 of them) were this issue, replaced it with a genuine bmw part and all fine!!!
only issue with the MAF is mine is located behind bumper and headlight so they have been off many times in this episode!!!
Moral of the story is that genuine parts are expensive but in some cases are the right ones for the job.
