Where does this vacuum hose go?

[chemprof]

Hey there, I just bought my first E30 (1989 325i convertible manual) yesterday!

But, it's got a blocked off vacuum line that'll cause a fail on visual inspection for California smog-check.

The line is in the right side of the throttle body, just above the one that goes to the brake booster. Anyone know where it's supposed to lead to? I can't find a good diagram in the Bentley manual.

Also, any idea why it would have been blocked off to begin with?

I've attached a picture.

[uturn]

You have the wrong brake booster check valve. The correct one will have a double to fit that hose. I priced a new check valve from BMW for my M30 motor, $80. Sure some one here will sell you a used one for way less.

[chemprof]

It looks like this one...

Part #: 34-33-1-158-113-BOE

So, my question is...A and B go to the throttle body, C goes to the brake booster, where would D go?

Thanks for the help. It's hard to troubleshoot a system when you don't know what it's supposed to look like.

[uturn]

I'll have to look mine over but I believe it's open to the air like a vacuum breaker. I could be wrong maybe it's supposed to be capped off and only used as a test port.

[jeffnhiscars]

They should both go to the throttle body

[uturn]

I looked mine over, I don't have that fourth port. I'm going to say it is a vacuum test port that needs to be capped off. You'll know for certain if you install it and it keeps drawing in air.

[vpilarrt]

I have a used but working 3-way valve and possibly some of the hosing if you're interested. PM me.

[chemprof]

Thanks for the offer! I'm waiting for the part right now. I'll post a follow-up when it's in.

[chemprof]

as a follow-up, my throttle body has two barbs for the brake booster. One goes straight to a three hole check valve, the other ties into the same valve and the throttle body inlet hose. There seems to be two throttle body inlet hoses, one for the straight ICV, and one for the bent one.

It seems that both work just fine, not really sure why BMW designed two similar systems, but I failed visual inspection for California smog with a capped off hose. After restoring to factory parts, I have a "stock" looking engine.