CIS Deceleration Valve

spencejm · 03-21-2007, 09:11 AM

I'm kinda sorta working on a high idle problem on my '82 SC. The car starts fine and when cold idles around 1800-2000 RPM. Once warm it idles fine at 1100-1200 RPM. I'm not real worried about it at this point but I did notice that there is a line missing from the CIS Deceleration Valve. I have looked at the CIS Primer on the Rennlist site and it looks to me like this is called the Actuation Line. From the vacuum diagram it appears to connect at the throttle housing. It also looks like the cruise control Ts into this same line at some point.

Does that sound correct? From reading the theory and description of all these parts it seems to me that reconnecting this line may actually make the idle higher but I do want to at least start any troubleshooting with everything hooked up correctly.

Should I be able to replace this line without too much difficulty?

On a semi-related note, I'm assuming that if this line is not connected my cruise control probably won't work (it doesn't.)

Thanks for any insight you can provide.

Joe
Columbia, MO
1982 911SC Targa

Gunter · Gunter's Garage

Some people confuse the AAR with the AAV, or the AAV with the Decel. Valve because they look the same.
Lots of vacuum lines tie into the TB.
Get the Bentley SC Repair Manual, you'll love it!

spencejm · 03-21-2007, 11:12 AM

I've got the Bentley and couldn't tell where the line went from the pictures. If you go to http://members.rennlist.com/jimwms/CIS/CIShome.html and look at the bottom 2 pictures in the Parts ID section you'll see what I'm talking about. I may have them confused. The two valves look almost identical but one has the small nipple. That's the one I'm talking about.

The Bentley manual pictures show this thing and the small line running across the front of the engine but the picture is cut off and does not show where it terminates. At least I was never able to find anything.

Thanks.

spencejm · 03-22-2007, 04:49 AM

Any help?

RoninLB · 03-22-2007, 05:44 AM

My deceleration valve malfunctioned and sometimes kept the idle high. I disconnected the vacuum line that removes its operation.

your high idle may be a vacuum leak on the fuel-air mix. If you can't lower the idle with the idle screw when it's warmed up to around 800 rpm I'd look for a leak. I always liked a CIS idle of 1k.

Gunter · Gunter's Garage

Quote:

Originally posted by spencejm
I've got the Bentley and couldn't tell where the line went from the pictures. If you go to http://members.rennlist.com/jimwms/CIS/CIShome.html and look at the bottom 2 pictures in the Parts ID section you'll see what I'm talking about. I may have them confused. The two valves look almost identical but one has the small nipple. That's the one I'm talking about.

The Bentley manual pictures show this thing and the small line running across the front of the engine but the picture is cut off and does not show where it terminates. At least I was never able to find anything.
Thanks.

I see what you mean. The diagram shows the Decel.Valve #15 as it is on'78-'79 SC's. There is nothing showing how the newer Decel.Valves look.
For '80-'83, the Decel.Valve looks very much like the AAV.
In your case, the AAV has the nipple and a small vacuum line would go the Thermal-valve #24 (if you have one) with a T to the WUR. I need to confirm this.
I disconnected the small vacuum line from the AAV and left it open without problems. I also run with Lambda intact but OX sensor disconnected.
Re Cruise control. I think it just has a T from the brake vacuum line? Not sure, someone else may know.