Paul, I actually just bought the car in May of this year, and immediately rebuilt the engine. Looking back on it now, I probably should have replaced the CIS hoses and intake boots at the same time.

I did check my AAR, and it appears to close fully when the car is warmed up. However, I'm probably going to try and clean the disk to make sure that there is nothing gunking up the seal. You are also correct about the Decel valve and AAV, and both hoses on both are connected.

You have vacuum lines attached to both the decel and the aav? You should only have the AAV hooked up. I know it's deceiving in that they both have nipples on the 80" but only one gets hooked up. In fact if the decel valve is getting vacuum you will get a very high idle. Later in 81 they went to a pancake without a nipple.

These vacuum devices can cause the type of problems you are having, but as others have said, there are other causes for leaks. Check the airbox, pop valve, injector seals, etc.

Most often though that decel valve is the cause of a high idle. As Scott says, you can try disconnecting one of the small hoses from the end of the valve and see what happens. It may bypass the problem. You may get a quicker return to idle speed, which some people like, and/or you may get a slight burbling from the exhaust or intake when the throttle is snapped shut.

Apparently squeezing the valve in the vice about 1mm was the factory fix for this.

You might try capping the valve nipple and/or just plugging the line w/ a bb and reattaching it.

Check Jim Williams' K-Jetronic site on rennlist. It's extremely thorough.

When disconnecting the hose to the decel valve, do I need to just block off the vaccum hose, or also the nipple on the valve?

smessing, did you ever got the fix to this?
thanks

I just solved the idle problem on my 1979 911SC from some hints from the forum.
I found that my linkage that went to the throttle body wasn't letting it closed completely. I legthened the accelerator rod a few turns out and that seems to have solved my 1 year idle problem. I was tinkering with the mixture and the idel screw getting it right only to have it increase when the car had been run for 1/2 hour.

#1, thank you. I had a high idle issue when warm up. Idle would increase to around 1800rpm. After replacing distro vacuum hose idle is now perfect around 900rpm.

Thank you

One more note,
 

This is a great thread an it finally helped me adjust my mixture properly. Just a note that is not mentioned, the mixture screw that is down inside the air box between the fuel distributor and air valve IS A FLAT HEAD on my 1980. I figured this out after poking for 1/2 hour with a bunch of allen wrenches.