CIS strange do'ins
 

I have two SCs acting exactly the same. I could use a little debug help with a CIS issue.

Both run well 98% of the time. Then randomly when power is reduced they fall below idle Rpm and quit. It looks like it may be temperature related since it started when it got colder. One is a 78, the other a 79. One has 70K miles the other 149K miles. Fuel was bought at different stations. One is high test the other mid grade. I cannot duplicate situations where it will happen. Ideas anybody?

Note: it is the random that is getting to me. They can run all day without problem and then you come to a stop light and blah, it quits.

Cis
 

A lot of posts on this. For a simpelton like myself I'd richen the fuel mixture (between fuel distributor and air boot - 3mm hex) a 1/16 of a turn. Solved it for me.

Other more in-depth considerations:
(1) check for vacuum leaks
(2) WUR (warm up regulator) is out of adjustment
(3) AAR (auxiliary air regulator - I have a 76 911S - Think it's the same for you) might be stuck open or closed

This is a short stab at the solution. But I recall having read posts that seem to share your exact problem. Sorry I can't locate them off hand.

Cis
 

I should be a little more clear.

Richening fuel mixture will help car when it's cold b/c CIS utilized several components to "richen" mixture until it is up to temp (WUR, AAR, etc.) - these components may not give the car enough juice when cold.

Oh . . . there is a particularly good thread

http://forums.pelicanparts.com/porsche-911-technical-forum/232089-cis-idle-speed-mixture-setting-without-analyzer.html?highlight=cis

Search under Souk - he knows his stuff better than I.

buy a fuel pressure gauge to check pressures. on cis pressure is everything

agree