1979 911SC Stock Motor-Idle bounce question
 

OK, so my 911 has always started immediately with a touch of the key. I've always been impressed at how easy it starts. Recently the motor was out and had some work done. All was running well.

then this...

After maybe 2-4 minutes of ciity driving, stop and go, driving along quite mellow, I came to a stop light pushed in my clutch and my idle went from about 900 to 0, car died. I started it and it idled then died. i started it again, light went green and with my foot on the gas pedal to prevent the car from dieing made it through the light, next light i came to it died again. As i started it again, and this time I was on the freeway by now, I pushed in the clutch and the idle dropped to about 200 then up to 2000 a couple times. By the time i was driving a good 20 minutes it seemed to get a bit better. but it still dropped off when I came to a stop it just did not drop off all the way.

I took it to the shop and they adjusted the mixture. I left the shop and the car did OK again for about 5 minutes or so then at a couple stop lights dropped low and almost died a couple more times, and one time it died.

Thought since I was at 1/4 tank, maybe more fuel would help. I run mid grade. 87 I think.

Anyone have any ideas what could be up here? I think I know why i have no problems in the 1st few minutes, something to do with cold start? but some clarification on the system would be greatly appreciated.

Any one see any problems with 87 octane? Also, it has become cold here in Colorado, and it seems to coincide with temperatures outside, but i'm not convinced it's the sole problem.

Perhaps my fuel mixture not quite right still?

87 is not mid-grade. 87 is cheap. midgrade is 89. premium is 91-93 depending on brand/location.
I run 92 (premium) chevron ONLY. I will drive out of my way 20 miles for Chevron Premium. I dont know if this is your problem. Ill let the experts weigh in, but I wouldnt use 87 gas as it could contribute to other problems.

I run nothing but 87 in my '79 SC as it has the stock, fairly low compression pistons in it. Premium is a TOTAL waste of money in cars that were designed to run on 87. As soon as you mod the engine (advance the timing, raise the compression ratio, etc..... then you may require higher octane to prevent detonation).

Your idle problem could be a number of things, but have you to tried simply turning the idle screw a bit to raise the idle speed?