Vacum hose going to brake booster

[genphreak]

Why necessarily block the nipple? Josh says that the valve must be carefully matched to the application - perhaps the sucking action is vital?

No way, you must block it. It is drawing unfiltered, unmetered air- it could even draw in sand if you dove through a sandstorm. Can you imagine BMW allowing this?

The reason the nipple is there is as a source of vacuum (used only in small amounts, so small the motor does not notice) for powering dash vents on some e34s. Most have motorised environmental systems, which is why this nipple is usually plugged, until the plug comes off...

What happens is the cap gets brittle and just falls off or someone snaps off the whole connector (unwittingly or stupidly) whilst fixing something else.

The hole is so small that no-one notices, except a month or three later when the car isn't running right and a technician takes a look (who possibly misses the leak). Few know enough about these cars to look for that, espeically ifg it is missing.

To get the car running correctly, they pull the AFM's air bleed bypass bung (which should never be removed or adjusted in normal maintenance) and wind it up so no air bypasses the AFM flap at idle. Thus all the unmetered idle air the engine needs comes from the hole in the brake line.

After that the engine stalls once you block the hole.

t_marat, you might like to check this out- see if I am right. If you had an AFM I would tell you to find your idle air-bleed adjustment screw. Use a 5mm allen key to wind it up (note whether the bung is still installed or not- if it isn't you can bet the thing is badly adjusted.) If it is, consider not touching it in case I am wrong. if you do adjust it, run it out 2 full revolutions (exactly) and then see if the engine stalls when you block the vacuum hose hole...

But you don't have an AFM on your car- yours uses a MAF right? Best look up where to adjust idle air bypass (don't think it has it) or perhaps they just call it the CO (carbon monoxide) adjustment. Or perhaps its automatic- the ECU might do it on the fly for all I know. In that case, block the plug, do a shogun reset or unplgu the MAF and run the engine until it notices the MAF missing. Plug the MAF back in and see if she then idles okay... Nick

No doubt someone will tell you to do it a better way, I've not messed enough with MAF EFI before...