Thank you so much! My newly purchased 335i has been in limp mode the whole time I've been driving it (over a month) because of a cracked boost line. There was enough slack to cut the cracked portion off (near the nipple) and reconnect. As soon as I did that, no more half-engine light, no more limp mode, and it drives like a completely different car, FAST.
A few side-notes:
1) My bluetooth ODBII scanner, connected to Torque (Android, Samsung GSIII) showed no fault codes after half-engine light, and all sensors/tests checked out fine. To access the fault code, I had to use the onboard computer (click up/down on the shaft arrow button until "check controls" was highlighted, select with the push button, then hold the push button down for 5 sec to display: CC-ID 29). Even though the Torque/ODB-BT adapter didn't detect that code, it performs wonderfully in general, and the adapter only cost me $25 (p!rated the app but will probably pay now because it works so well). The boost sensor now reads 4-5 psi under moderate engine load.
2) The stock lines are not suitable to withstand the temperatures generated in that area. My lines looked totally decrepit, cracked near the nipple coming off the engine, and will have to be replaced (with heat-treated silicone lines) once I have the time/they crack again. They are totally brittle. I had to spit on the nipple to get it back in (huh-huh...LOL!!!).
3) BMW sucks for not making the rear two engine cover hex bolts accessible without taking off two air intake/engine cover cowls/manifolds (about ten 5/19 in bolts, took an hour to take off/reattach). Those two allen bolts are never going back on my engine cover as long as I own the vehicle.
4) Now I only have to get Carmax to replace the rear passenger window regulator. The damn thing (green piece that the cables attache to) snapped (i thought the glass had cracked lol!) I already removed the door panel, peeled back the foam lining and stuck a c-clamp / vice on the runner to hold the window up as it is freezing right now and, at high speeds, having one rear window open generates resonance that makes it sound like you're driving through a wormhole.
Thanks again for your post.