In my quest to solve my irregular idle problem, I plug my new duty cycle meter quite often into the diagnostic terminal X11 (pin #3).
Interestingly enough, when the crappy-oscillating (500-900 RPM) idle is at work I get the dancing duty cycle (27-33%). Which means the elements in the closed loop are working (right?)
Now the funny part, when it finally settles at normal steady idle
(about 600-650 RPM) the duty cycle stops at a fixed number (60.4%). This means there is a fault.
In the website I mentioned before, 60% fixed at idle means there is something wrong with the CMP sensor (L5/1). Lets not forget the disclaimer, these are codes for 1993 or newer. (I am assuming they are the same for mine since they are taken from the same diagnostic pin)
Questions:
What is the CMP sensor (L5/1), what does it do?
Where is it located?
How come it actually shows a fault when the idle is steady, while no faults while idle oscillating?
If I have a vacuum leak, and it is causing the problems described previously in the thread, how come is not permanent?.
Is there such a think as an intermittent vacuum leak that comes for a week, creates havoc with the idle, leaves for 3 weeks and reappears, and so on and on?

PS. Unfortunately they are predicting rain or freezing rain for the area. Which dims my hopes of playing with the idle control mixture screw. I'll still test the O2 sensor from inside the car.

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1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
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