Thank you for this DIY. This Helped fix my idle and got rid of the "turbo whistle..." I have a 99 E46 328i. My intake boot was very badly cracked, i'm surprised something worse didn't happen. I mean you can see through the hole.
This has been a probably for me for the past 40k miles, I've just overlooked it many times. Now that it's fixed, it seems as though my throttle response has increased. But on the other hand, my MPG dropped from 26 to 24. I have only driven close to 20 miles since the replacement.
I was thinking, this may be the MAF adjusting to the change? Does this sound remotely correct?