Auxiliary Air Valve Repair

[wa3vez]

After considerable CIS work on my 1976 911 it was running fine. However, the idle was all over the place from 700 to 1600 rpm when I stopped for a traffic light. Occasionaly it would stall out when it went down to 700 rpm. Sometimes it would be at 1400 and then drop to 1200 then 900 in about 2 sec while waiting at the light. On occasion it dropped to 900 after warm-up and stayed there (as it should).

After a number of tests I tracked the problem down to the AAV. This valve is just a horizontal plate with an air input above and output below which adds air to the CIS system to provide increased speed for a cold engine. The valve plate shaft was sticking and therefore not always completely closing when the engine had reached temperature. I checked the cost of a replacement valve and immediately decided there must be another way. So I had an idea based upon someone on the forum that had tried PB Blaster.

The valve is in the back of the engine on the left side and hard to reach without removing several large components. So I decided to try a different approach. The top of the valve is easily accessed so I removed the input hose (hose clamp). I then plugged in a small piece of scrap hose (about 6 inches long) since the top of the AAV was just a few inches from the top of the engine compartment. With a hair dryer I heated the AAV till the plate would close and stay this way for 30 or 40 seconds. I then sprayed some PB Blaster in my hose and let it sit overnight. The next day I re-installed the factory hose and so far the idle has been solid at 900 rpm.

My AAV does not have an electrical heating element which helps the valve close after the engine reaches operating temperature (this was added in later models). Since this involves no large expenditures, does not require the dis-assembly of any engine components it is certainly worth a first try.