Next I tackled the injector vacuum "tree" which is getting notorious for hard, brittle hoses that crack. See elfhearse's picture above! Mine were not as bad, but were definitely starting to crack. They were also getting extremely hard.
Following elfhearse's advice, I found the Goodyear 5/16" (7.9mm) fuel/emission hose to be a
perfect fit. I suggest slicing the old hoses off with a razor.
Cut replacement hoses from your 3' section of emision hose and reassemble the tree. You'll need no more than 2' of the Goodyear emission hose which will be under $2.50. You can also buy a new tree assembly from BMW for about $26. Replace the larger vacuum hose that runs from the tree to the intake boot as well.
Orginal tree.
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Hoses removed
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New hoses fitted. The tightly bent hose is a little finicky because the factory hose is molded to that curve, whereas the emission hose kinks a bit when you bend it that tight. It takes a little squeezing/working of the hose to remove that slight kink. That's the only downside I can think of by using the Goodyear emision hose vs. a new factory tree. Thankfully you can make the curves of your replacement hose larger than the factory hoses as there's no need to make an EXACT reproduction of the factory hose. All this is doing is carrying a little vacuum.
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After that, I used the remaining portion of the emission hose to replace the section that runs from the throttle body to the "fuel tank breather valve". Not sure what this valve does, but it's electrically controlled and it sits between this vacuum hose and the carbon filter.
The hose in question:
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Simply replace this hose with the remaining emission hose. The original hose is molded to keep it from touching the alternator. I found I needed to use a little electrical tape (or zip tie) and attach it to the bottom of the intake boot to provide clearance from the alternator.
While everything was out, I also replaced the o-ring that seals the DISA valve to the lower intake manifold. Just remove the three bolts holding on the DISA valve, use a pick to remove the old o-ring, and install the new one using some synthetic caliper grease. Make sure you clean the bore the DISA valve goes into first with a clean rag.
Also, use a pick and replace the tiny o-ring that's in the hard fuel rail connection. Probably not necessary, but might as well as you have everything apart.