[Michael335d]

I dropped my car off at the mechanic next door to try and find this Underboost condition. Here’s some history. Last time I took my car to the Stealer, they forgot to bolt down my cabin air filter box. Also, my hood would not open on passenger side, I had to use a screwdriver to open hood. Anyway, shortly after I picked up car from Stealer, I was diagnosed with Hodgkins Lymphoma at 40 years old. I’m in remission now and say I should be cured so it’s all good. Anyway, I didn’t drive car for a year while doing treatments/recovering. So when I had the b+ cable fry out, I had to replace fuse box and part of cable, that’s when I noticed hood wouldn’t open, and when I did open it, I noticed they forgot to screw down the cabin air cleaner box COMPLETELY. No screws present, they just put cabin filter box there and closed hood!!!! I complained to BMW, but since time elapsed and it was their word vs mine, they made me BUY THE SCREWS which were $12. I promptly installed screws. Now with this underboost condition, reduced engine power, NO POWER FROM SMALL TURBO, I’m wondering if I crushed a vacuum hose since one runs behind cabin air cleaner. I can’t get to my car until morning. Cabin air filter box is still loose because there were 2 screws and metal bars holding the front of the cabin air box, and they are still missing. IM following turbo vacuum line diagram, and it looks like hose runs right under cabin air filter. Any thoughts? Still getting full boost from big turbo. I did smell burning plastic when defroster activated while in Reduced Engine Power mode. I’d be doing most of the work myself, but have bad neuropathy in hands from chemo, so I have to rely on friends and this forum for work and advice. Thanks a million guys. All these problems is better than being 6 feet under, so I’m not complaining..

[335stoner]

do you have any engine codes? I do not think it is possible to pinch a line with the cabin filter...

if I am not mistaken things to look at are
-vacuum lines
a lot are near the turbo range and they go bad and leak
-pressure converter
this is near the back of the motor and can go bad.

here is vacuum line replacement
http://www.e90post.com/forums/showthread.php?t=1255573

here is the converter replacement
http://www.e90post.com/forums/showthread.php?t=1308500

I'm sure the brains will chime in soon

[JuiceQuadre]

to OP:
maybe you are mistaking the air filter for the cabin filter? there is a line going sort of underneath the air filter but i think its for the wastegate which would just cause the wastegate to not open but you would have different symptoms i think..

[rbreding]

Agree with other posters. No vac lines near the cabin filter up top. As others said......likely an issue with some vac lines or converter. Need codes.

[335dlci]

Originally Posted by rbreding

Agree with other posters. No vac lines near the cabin filter up top. As others said......likely an issue with some vac lines or converter. Need codes.

Yeah where are these cabin filter vacuum lines. I have never seen them on any e90. Gas or deisel.