Missing Vacuum hose

[Vancouvertechie]

Greetings,

I am a new Porsche owner and my 1981 911SC idles rough when cold. Only until the temperature hits 190 does it idle smoothly.

My friend pointed out a missing vacuum line. Can anyone tell me where it goes?


You can see it in the upper right hand corner of the photo.

Thanks,

John

[ossiblue]

That is the auxiliary air valve which should provide by-pass air to the engine during cold starts. The vacuum line connects to the intake manifold. With a mirror, look behind (toward the firewall) the ribbed intake boot at the top, center of the picture. You should see either a loose hose back there, or the nipple where the hose should connect. (Note: the connection is not on the rubber boot but is a separate part for vacuum that is located in the area I described. I'll see if I can find a picture that shows it but in the meantime, here's a diagram that might help: http://members.rennlist.com/jimwms/CIS/CIShome.html) Click on the link, then click on "vacuum diagram." You're looking for part #10.

[Vancouvertechie]

Originally Posted by ossiblue

That is the auxiliary air valve which should provide by-pass air to the engine during cold starts. The vacuum line connects to the intake manifold. With a mirror, look behind (toward the firewall) the ribbed intake boot at the top, center of the picture. You should see either a loose hose back there, or the nipple where the hose should connect. (Note: the connection is not on the rubber boot but is a separate part for vacuum that is located in the area I described. I'll see if I can find a picture that shows it but in the meantime, here's a diagram that might help: CIS Primer for the Porsche 911) Click on the link, then click on "vacuum diagram." You're looking for part #10.

OSSIBLUE,

Thanks for the reply and I will check this out tonight. I hope that works, but the strange thing is today the car idle pretty nice this morning. But the air temperature was warmer in the garage.

John

[arbita1]

That's actually the deceleration valve, not the aux air valve. It keeps the RPM's up on deceleration. The line should be in the back connected to a "T". Take a camera and take some pictures back there...you be suprised how much that help you see what's going on back there.

At any rate, even if the line is sitting back there unplugged, I don't think that will affect your rough idle. It is probably something else.