535 Air Intake Leak?!?

[renegade]

Can anyone help? I've got a '92 535 sport that drives fine but Idles at 2000rpm when warm and is lumpy and stalls when cold. I have been assuming that the problem is an air leak, but can't find one. The air flow meter, Idle Control Valve and the bellows linking them to the throttle housing have all been replaced. The dipstick seal is also OK, have tried spraying wd40 everywhere to trace a leak but it's not helped. Can't hear any hissing because its revving too high!

There is a small split in the pipe between the Air Filter and the Air Flow Meter but I've been told that this is outside the vacuum area. The throttle seems fine and not sticking. I read somewhere that the engine should stall when the oil filler cap is removed, but it makes no difference to the idle, the seal seems fine here aswell.

Any Ideas?

[Martin in Bellevue]

• Check the breather hose to the valve cover? This hose has a small vacuum hose T'd to the lower, hidden part of the aluminum intake manifold.

• There is also another small vacuum hose on the underside hidden part of the intake that connects to the fuel pressure regulator at the front top part of the motor.

• There is a potential air leak at this underside part of the intake, where a larger hose connects to a switched valve pulling vacuum to the charcoal cannister. This thing never gets attention.

• Don't forget to check the hose to the intake from the idle control valve. It is not too fun either.

http://www.bimmer.info/bmw/Martin5er/m30maf.jpg

[Bill R.]

1
• Check the breather hose to the valve cover? This hose has a small vacuum hose T'd to the lower, hidden part of the aluminum intake manifold.

• There is also another small vacuum hose on the underside hidden part of the intake that connects to the fuel pressure regulator at the front top part of the motor.

• There is a potential air leak at this underside part of the intake, where a larger hose connects to a switched valve pulling vacuum to the charcoal cannister. This thing never gets attention.

• Don't forget to check the hose to the intake from the idle control valve. It is not too fun either.

http://www.bimmer.info/bmw/Martin5er/m30maf.jpg

[Derek A.]

I would try using carb cleaner instead of wd40 to search for air intake leaks.

[Karl]

It might be an engine gasket someplace, since the whole thing runs at manifold vacuum.
- valve cover gasket
- main seal (rear main was my culprit, but I guess it was due for a clutch anyway)

[Mobius]

•StuffMartin - ya forgot the worst one. :)

http://home.comcast.net/~rjchristie2/SA/535i/IMG_3284s.jpg

[Martin in Bellevue]

It sounds like that unconnected vacuum hose should fit into the nipple off the breather hose. The breather hose is between the valve cover & the inlet hose in front of the throttle body, as shown. The nipple for the vacuum hose normally points down & is further hidden by the intake manifold.

http://www.bimmer.info/bmw/Martin5er/breatherHose.jpg

Yeah Moby, I did forget about that nipple off the vacuum hose to the brake booster.

[George M]

did someone say Nipple?
:)

[renegade]

Cheers
Have checked them out, they both join the bottom of the intake manifold.

I found another one tho just hangin loose, it was down by the starter motor