Anyone interested can simply look up Audi TD1, and read all about how Audi started catching previously "undetectable" tunes. They leverage checksums in the software, among other things. Basically there are a range of checksums that can be "ok" and enable the car to run. Within that range though Audi has a specific set that must be exact, based on the version of the code you have in your ECU. Any variance from theirs flags your car as TD1...meaning the ECU was tampered with. The ONLY people permitted to flash an Audi ECU and not void the cars warranty are Audi. And when they do it they track which tune is in it. They will even flag you car TD1 even if a factory tune is currently in the car....if that tune is one they had already flashed out (meaning they installed a different version I'm your car at some point). The worst part is when you car is flagged TD1 Audi flags most of your warranty as void. This includes the ECU (obviously), the electrical system (because it is connected to the ECU), the Engine/exhaust/emissions, the tranny, the diff's....don't take my word for it (as a previous Audi owner) read up on TD1....

Yes, their are several laws that prevent this, and should limit Audi to only being able to void the ECU warranty...and maybe a few obvious parts. And yes, these same laws require Audi to PROVE the ECU tune caused the issue they are refusing the warranty BEFORE they do so.....and the reality is Audi has more lawyers than most of the companies we work for have employees, and then include the dealers own attorneys...we are talking tens of thousands world wide....and they have DEEP pockets....so unless we want to get a lawyering fight them in court (which no one ever does) they win.

Now BMW may not be as advanced or draconian as Audi has become.....I am not as familiar with BMW's behavior yet. I just believe in making informed decisions, and there is no reason BMW cannot do the same thing as Audi (and all the VAG companies (Porsche, Bentley, Lamborghini, VW, Skoda, etc) are doing.

So....as I was saying...if you have factory warranty left I thought not tune. If you have an extended warranty (factory ENVER offer this, they are dealer sold items provided by independent warranty companies) check with them first. If you are out of warranty, go for it. Tunes can be a HUGE gain, and when done properly are amazing and do not harm your vehicle at all. As has been mentioned though, a tune from a fly0by-night shop can do a lot of damage.