CIS operation

[930turbo]

I spent about a year fiddling with my CIS in an attempt to resolve a rich at idle condition. I was about to commit to a fuel head and WUR rebuild when by chance I discovered the real problem. The trigger wire plug from the distributor had a bad connection. I replaced this wire and completely rebuilt the wiring harness on the engine during the rebuild 7000 miles ago so I assumed there would be no issue there. I pulled on the wire while the car was idling and it died. When I checked inside the plug, it was green. Apparently it got wet somewhere along the way. I cleaned the connection and the problem is solved. The signal from the distributor weakens as the engine slows. It had a mis-fire at an idle that sounded like an old small block Chevy with a large cam. It smoothed out as soon as you increased engine speed above idle. The over-rich condition was caused by the asymmetric mis-fire @ idle. If your car doesn't sound like a 911 SC at idle, check your ignition. My lesson learned, don't necessarily blame your CIS.

[A930Rocket]

With our cars getting up there in age, all kinds if stuff can to wrong, even with low mileage examples.

Glad you found the problem.