We have confirmed the following with BMWNA and is in fact an official response to complaints about turbo lag. Models affected are the 135i, 335i/xi, 535i/xi and the X6 xDrive35i.
The turbo lag is not overwhelming for most and to some it is not noticeable. The cause of the lag is due to a change in the engine software; some were built with the new software while others obtained it through an update at the dealer. The reason BMW was updating the software was because of certain noise concerns and the by-product of the update was the increase in lag and the desired decrease in noise.
For some time the lag was denounced and was never officially acknowledged; this statement changes all of that. It also indicated engines may be updated with software that does not cause lag but may cause this “noise “. We would think most enthusiasts would welcome the noise over the lag but for certain others it may be the other way around. You apparently will have a choice.
“In an effort to address specific noise concerns, BMW updated the turbocharged engine software on 335i/xi and 535i/xi models built from June 2006 through March 2008. The updated software causes a small amount of increased “turbocharger lag” under certain circumstances and, while not substantial, the lag may be perceptible to the most sensitive BMW drivers. X6, 135i, and 3 Series/5 Series vehicles from March 2008 production onward are not affected. Release of the new software to restore the original turbocharger response is planned for January 2009, and it will be available for vehicles produced from September 2007 through March 2008 when they are brought to an authorized BMW center for a repair which requires a programming update. Clients with vehicles produced from June 2006 through September 2007 may request installation of the January 2009 software update. Clients who get this update should understand that there is a possibility of slightly increased engine noise levels under certain circumstances. ”
We would like to thank our friends at the BMWCCA (especially Satch) for initiating the movement for and obtaining the official statement. Further information will also be in the January issue of Roundel (join the Club!). Thank yous go out to our other sources for helping us confirm this information; we appreciate it!
When we have more specifics we will provide you with them.