Brake Booster Vacuum Line Check Valve? (Pic)

[digger]

arrow points to engine side (it says on the valve) so white to booster and black to engine. suck and blow on it will also confirm this

[Albinoe30pnw]

This weekend we ended up testing out exactly how the stock 3 nipple check valve works. It's actually pretty impressive.

Air can flow from the single nipple on the brake booster side to both the pre-throttle body (TB) and post-TB nipples on the engine side. That's the direction of the check valve.

Air can't flow from either the pre-TB or post-TB nipples into the brake booster. This is expected. Now here's the cool part. Air can't flow from the pre-TB nipple out the post-TB nipple, and vice versa. So the check valve as a whole is actually like two separate check valves packaged in one.

Therefore if you want to use a 3 nipple check valve like a two nipple check valve, all you have to do is use a piece of the factory rubber hose on one of the two engine side nipple, and plug it with a 0.5" OD round (1/2" stainless/alu/mild steel rod works nicely) object. This is what we did.

Sorry to bring up an old thread but just recently acquired an 88 325 2.7l and was going through to diagnose low idle issues and noticed my "check valve" is the exact same as yours. And was wondering if you could post some pics on how you did it exactly. Thanks