Vacum hose going to brake booster

[t_marat]

I have one nipple sucking in air, as shown in the picture. At first I blocked it off, idle become a little more smoother. I did it so because I saw Wingman's post before where there was a nipple like that and that was blocked. But the idle became completely unstable once the engine is fully warmed up (temperature gauge in the middle). It just stalls. Openned again that nipple, and it does not stall anymore.

Link to that post:
http://www.bimmer.info/forum/showthread.php?t=20681&highlight=vacuum

In those posts it was stated it is used to draw air over the temperature sensor. The same for me? Mine looks a little different.

[wingman]

mmmm interesting. The first time I got my car up to full operating temp after closing the hole up I got a couple of big misses when doing about 110kph (65mph). Since then the problem has gone and I'm happy with the performance. The idle is still smoother and no adverse effects. You may have another issue.

[genphreak]

I have one nipple sucking in air, as shown in the picture. At first I blocked it off, idle become a little more smoother. I did it so because I saw Wingman's post before where there was a nipple like that and that was blocked. But the idle became completely unstable once the engine is fully warmed up (temperature gauge in the middle). It just stalls. Openned again that nipple, and it does not stall anymore.

Link to that post:
http://www.bimmer.info/forum/showthread.php?t=20681&highlight=vacuum

In those posts it was stated it is used to draw air over the temperature sensor. The same for me? Mine looks a little different.Definately it should be blocked off, unless it was used for running the cabin's ventilation flaps (you'd know the ventilation/demister etc would not be working properly). In which case find/repalce this pipe and reconnect.

Otherwise you should block it off and try a Shogun's reset procedure. (search is your friend) whereby the car's engine computer (ECU) is reset. Basically you disconnect power to the ECU for a short period and it forgets its learnt data, returning to factory defaults. ON reconnection and some driving it learns your engine anew. :)

If this doesn't work and it still stalls, someone has probably adjusted the Idle air bleed screw on the Air Flow Meter right up (thus making up for the air drawn in from that damn little pipe after the original bung came off). Or maybe your motor has other settings... maybe idle? Check the Bently for details on how-to do all this... Don't fret about it if so, if it is the case it shows your motor is has no OTHER vacuum losses (ie intake leaks). This is a good thing as many have had to battle hard to find leaks...tho more suspect them for other reasons...
;) Nick

[t_marat]

What that white thing is? Here is a diagram:
http://www.realoem.com/bmw/showparts.do?model=HB51&mospid=47370&btnr=11_1124&hg=11&fg=40
The only thing I can see is the temp sensor. But as visible in the diagram, it is at the middle of the throttle body. But that white thing is located a little higher than the throttle body.

[genphreak]

What that white thing is? Here is a diagram:
http://www.realoem.com/bmw/showparts.do?model=HB51&mospid=47370&btnr=11_1124&hg=11&fg=40
The only thing I can see is the temp sensor. But as visible in the diagram, it is at the middle of the throttle body. But that white thing is located a little higher than the throttle body.Non return valve. Stops your engine copping the changes in pressure from the brake booster when you brake or if it fails. I replaced mine when I broke the pipe off, it cost a heck of a lot at the stealer over AU$50, man was I ripped. Every now and then they find a way to get me, it's just life.

[t_marat]

Sorry, but what does "copping" mean?

[joshua43214]

Sorry, but what does "copping" mean?

Copeing with means to deal with.

Also the description is a bit misleading. It is a check valve that maintains high vacuum in the power booster. You will notice the little arrow embosed on it, this points in the direction of air flow, which is from the booster to the engine. This valve allows you to have full power brakes in the event that the engine stalls or in low vacuum situations. If the power booster fails, the engine will draw air from it and you will have a large vacuum leak.

[t_marat]

If the power booster fails, the engine will draw air from it and you will have a large vacuum leak.
That is if the power booster fails or if the check valve (non-return) fails?

[joshua43214]

That is if the power booster fails or if the check valve (non-return) fails?

If the booster fails, you will have a large vaccum leak that will pull right through the check valve, since it seals vavuum into the booster.

If the valve fails, the booster will not hold vaccum and you will not have power brakes in low vaccum situations.

the valve also has a built in restriction that "smooth's" out the demand from the booster. If you removed the valve from the circuit and punched the brake pedal the engine speed would dip suddenly and possibly stall, from the sudden change in manifold pressure. The restriction is matched to the aplication, so you must use the proper replacement part rather than any kind of universal booster check valve.

[genphreak]

If the booster fails, you will have a large vaccum leak that will pull right through the check valve, since it seals vavuum into the booster.

If the valve fails, the booster will not hold vaccum and you will not have power brakes in low vaccum situations.

the valve also has a built in restriction that "smooth's" out the demand from the booster. If you removed the valve from the circuit and punched the brake pedal the engine speed would dip suddenly and possibly stall, from the sudden change in manifold pressure. The restriction is matched to the aplication, so you must use the proper replacement part rather than any kind of universal booster check valve.Thanks Joshua for the details there, I was indeed more sepculating it did something interesting... your description is very informative. Now I feel better about spending $50 on it since it is so important... :) Nick

btw; by 'copping' I meant incurring, but we're all on the right track! My apologies also for using this Aussie slang word.

[t_marat]

Thanks everybody

[t_marat]

Had to resurrect this post.

Every time I block this nipple, the engine stalls when at operating temps (middle of the gauge). It drives OK, but when I engage the clutch and switch to neutral, it forgets that it needs to idle, goes directly to 0. Tried doing the reset, by disconnecting the battery for the whole night. Does not help.
If I remove the blockage from the nipple and let it suck air as it wants, the engine does not stall. But it needs to be blocked, I saw another BMW 525i, and that nipple is blocked in it by a rubber cap.

Can I safely presume the issue not being the ICV? If it was ICV, should not it stall with the nipple being open?

I read somewhere about a breather valve being the culprit. What do you think?

[Rustam]

Had to resurrect this post.

Every time I block this nipple, the engine stalls when at operating temps (middle of the gauge). It drives OK, but when I engage the clutch and switch to neutral, it forgets that it needs to idle, goes directly to 0. Tried doing the reset, by disconnecting the battery for the whole night. Does not help.
If I remove the blockage from the nipple and let it suck air as it wants, the engine does not stall. But it needs to be blocked, I saw another BMW 525i, and that nipple is blocked in it by a rubber cap.

Can I safely presume the issue not being the ICV? If it was ICV, should not it stall with the nipple being open?

I read somewhere about a breather valve being the culprit. What do you think?

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

[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...

[t_marat]

Well, there is another my thread on MAF resistance checking. I think my MAF is dead. When I unplug the MAF there is no difference in idle quality, absolutely none. I tried disconnecting the MAF after disconnecting the battery for the whole night, there was still no difference.
I think MAF does not have any idle adjustment screw. There is no blockage to the air, its not like AFM.

Maybe it is because the MAF is dead? But in this case the engine is supposed to run in limp home mode, which I think should still have stable idle.