Brake Booster Check Valve (BBCV) Boggle

[Zchild]

I recently discovered that my BBCV is broken and I trying to figure out how much this vacuum valve contributes to the idle of the vehicle. Thanks in advance for your help answering this boggle.

[JimLev]

You mean the jet suction valve thats between the brake booster and the CCV?
Depends how bad it's broken, the engine can stall or just run rough and throw a code.

[geargrinder]

First of all... lets explore terminology... While I won't jack you up too hard on calling it a "brake booster check valve".. its real official BMW name is "sucking jet pump". Apparently some parts vendors have taken to calling it this BBCV term I guess... but its definitely well more than just a check valve... its a venturi vacuum amplifier thing...

But if you want to search for info on it a lot of threads will call it by its proper name - the "Sucking Jet Pump". (not that the official name is that great either... but it is what it is...)

Now: Is the question "how much can a leak there cause an idle problem?" If so - as Jim says - depends, but could be as much as "a lot".

But, if the question is "how necessary is the sucking jet pump?" - the answer seems to be "not very". Some owners have deleted it and reported a virtually undetectable difference in brake effort. However, its supposed to be there, and its supposed to be an integral part of providing brake boost. I dunno. I'd keep it myself unless there's some overriding need to re-engineer it. You wouldn't want to find out that "its undetectable except under conditions of emergency braking from 70mph down to zero when hurtling towards a large fixed object and/or busload of nuns & orphans, in which case it suddenly makes a big difference".

[JimLev]

I'd have to look at the internal setup to know if this helps keep vacuum in the booster (probably does) if the engine suddenly dies. There are 2 "check valves" inside.