See first post.

I found it in the X3 by laying under the muffler and looking on top of the muffler for the vacuum pot--feel around the muffler outlet area--use a mirror if you have to not all models have the valve--on the X3 it can be seen looking through the tailpipe with a flashlight.

Some pics
 

Here are some X3 pics where to disconnect if you don't want to do it at the muffler.

I unplugged mine and immediately noticed a 20 hp gain at idle and below 2000 rpm ;) In the long run and during long trips the sound may be annoying but it's easy to plug it back if needed.

- p

Don't forget to plug the vacuum pipe that you took the hose off--Don't know if this will cause a vacuum leak or other problems

Per the suggestion on the first page, I just zip tied the hose closed as shown in the pictures. Very easy to do and no vacuum leaks. It was interesting to start it up with the hose pinched and then let it go to hear the difference in sound. Quite a change.

Also, if I didn't know any better, the engine feels a bit stronger. It's probably all in my head, but without a dynamometer to prove me wrong, maybe - just maybe - it is...

http://greggpeterson.com/aux_images/X3/GolfTee01.JPG

http://greggpeterson.com/aux_images/X3/GolfTee02.JPG

Ya know I thought I felt an increase in part throttle response but was afraid to say so--I completely forgot about the modification and I took the car out a day after I plugged the hose and --I noticed a different feel (similar to the sport button on my Z4 but more subtle) then I remembered I had plugged the hose--then I paid attention to the nicer sound from the exhaust--I will have to do an A B comparison some time.----Enjoy--Its a fun modification..:)

Thanks for the reminder. I got carried away and went for a test drive immediately after unplugging :) I have driven it unplugged for a week now and no issues discovered so far. Other than I seem to drive more and more every day...

For others thinking of doing this, the vacuum seems to be on the plasic 'nipple' side and not in the hose left hanging around (see the pic in my previous post). So it might be worth putting something there to fool the system. Or do the zip tie trick like X3eme did his.

I might check if there are any fault codes activated now that I drove it unplugged.

- p

Why are we doing this exactly? My understanding of the system is that it helps heat up the cats and O2 sensors when cold.

A previous post stated that its there for sound control only and it does do that--Many X3 don't have the valve--and of course I guess we can do this only if we want to at our own risk!:)

After living with the defeated valve for a day or two I would agree that the reason for the valve is sound control. Without the valve, the X3 does not sound like it has a refined 6 cylinder BMW engine. At low revs it reminds me of a bigger Honda engine with one of those huge aftermarket exhausts. It needs that valve to sound like a near-luxury BMW.

If I have hypothesized correctly, would it be a stretch to think BMW gave up a little power to get it to sound like it should?

I still think it feels a little... not much... but a weee bit peppier.