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Vacuum Hoses

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ron madden
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Vacuum Hoses

Post by ron madden » Thu Apr 21, 2011 5:23 pm

Hello Everyone,

My 635 has a rough idle but runs fine when I give it the gas. I am thinking it might be the vacuum hoses. Does anyone know where to find information on hose sizes, diagrams, etc. Even if this is not the problem, I still want to change them out due to age. Any other thoughs about what it could be besides a vacuum leak. Idle control valve, air mass sensor?
Thanks as always Ron

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Post by Brucey » Thu Apr 21, 2011 7:56 pm

it is most likely the vacuum hoses or perhaps another leak.

Best to buy the hoses from BMW or take yours off when you go to buy new hose by the foot.

Best sort out the vacuum hoses/leaks first before looking at other things, I'd say; there are many possibilities, but looking at these parts before you are sure about vacuum leaks isn't worthwhile.


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Chris Wright
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Re: Vacuum Hoses

Post by Chris Wright » Fri Apr 22, 2011 5:03 pm

ron madden wrote: .... I am thinking it might be the vacuum hoses. Does anyone know where to find information on hose sizes, diagrams, etc.
This applies to an '87 635, verify all of this by measuring your hoses before buying new hose.

I went down and bought 6 feet (If your car has the electric purge valve, it will be more like 3') of the 3.5mm ID black braided German hose at a local Import Auto parts house and I ordered the valve cover breather hose (they split underneath) and the ICV hose. Only remove, cut and replace one hose at a time:

Valve Cover Breather hose, note "Tee" molded into this one:

Vacuum Leaks:

Any air that gets in through a vacuum leak is un-metered air and it upsets the fuel/air mixture. If you don't think it can make much of a difference, just open the oil filler cap with the engine running. Here are some sources of leaks to check:

1) Valve Cover gasket (use a gasket dressing - Take the opportunity to adjust the valves if they haven't been done in a while.)
2) Valve Cover Breather Hose - Ref #11 (they crack underneath, some hoses have a nipple underneath and a vacuum hose leading from it, to the intake manifold). Make sure that the elbow Ref #10 on the breather hose has not popped out of the intake boot. A backfire can pop them out.
3) Rubber Intake Boot between the AFM and the Throttle Body - Ref #6
3) Vacuum Line for the FPR (not shown) and Purge Valve - Ref #19&22 (Unless you have the electric Purge Valve)
4) Idle Control Valve (ICV- Ref #3) hose Ref #8
5) Oil Cap seal
6) O-rings on the injectors, check that they aren't dried up by putting a little oil on them or squirting some water at the base while the engine is running.
7) O-ring on the dipstick
8 ) Check that the White Nylon line from the bottom of the intake manifold to the inside is hooked up to the manifold.

Hooking up the three vacuum nipples on the intake manifold:
On the square underside of the large aluminum intake, there are three vacuum nipples, the nipple on the edge closest to the fender can be seen and has a small piece of hose that connects to a white nylon line that leads to the interior temperature sensor in the kick panel inside. DO NOT replace it with a piece of the hose you just bought, it has a flow restrictor inside of it (see below*).

Observe any rubber grommeted holes in the manifold that the hoses pass thorough as you remove them in-order to replace them correctly. A photo might be helpful:

Now get out your mirror and flashlight and find the two nipples along the bottom edge of the maifold closest to the engine. The one to the front of the car goes to the Fuel Pressure Regulator - FPR (approx 17.5" long) and the one nearest the firewall goes to the "Tee" on the bottom of the valve cover breather hose (approx 12" long).

On cars with the vacuum purge valve, the hose runs from a nipple on the throttle body, to a plastic Flow Restrictor (Ref #21 - note the color of the half that goes to the TB), to the Purge Valve Temp. Switch (Ref #20) and then to the purge valve (Ref #19) (approx. 14" and 23" long).

If the image doesn't open

*Flow restrictor: 64 11 1 386 446 Ref #12 below (ref #10 is the interior temperature sensor and ref #11 is the white nylon line - yellowed to brown with age)

<a><img src="" border="0"></a>
<a>BMW parts catalog</a>
Last edited by Chris Wright on Fri Jul 27, 2012 1:54 am, edited 1 time in total.
Chris Wright
'87 635Csi
3 MGA's
MG 1100

ron madden
Posts: 38
Joined: Fri Nov 28, 2008 11:56 pm
Location: CA

Vacuum Hoses

Post by ron madden » Fri Apr 22, 2011 8:25 pm

Thanks for your sugestions. I have a lot to do.


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