Low idle at start, and sputtering....SC

Joe Bob · Joe Bob's Garage

1983 911 SC, CIS fuel injection.

Something new....when stone cold the engine likes to die when
started....takes two, three tries to get it to stay running and 20-30seconds to come up to 800 rpms. Once warm, restarts are fine, no other symptoms....

Any ideas?

john walker's workshop · 01-30-2002, 01:53 PM

classic warmup regulator problem. it causes the engine to run too lean when cold. first make sure the co is set to 3.5%, and the oxygen sensor is left unplugged. that should be in order before doing the regulator. just for the hell of it, unplug the oxygen sensor computer relay under the right seat, and see if, when warm, the idle gets wierd, and then recovers when you plug it back in. do a search for adjustable warmup regulator. they can be richened if you're careful.

lagoon · 01-30-2002, 01:53 PM

Check your warm up regulator with a CIS pressure gauge. It is most likely set too rich. 81'SC

Joe Bob · Joe Bob's Garage

Well, two answers....lean and rich....forgot to add that there is n O2 sensor, I am running SSIs and a Danske 2 in 2 out.

It ran fine after that mod, but started this problem recently.....

pbs911 · pbs911's Garage

I had this problem with my 78SC for a few months. I disconnected and cleaned all the electrical connections that relate to the CIS system and it works great now. Try the simple first.

makaio · 01-30-2002, 07:08 PM

Mike,
welcome to my world. My car has been doing almost the exact same thing. Without going into great detail, it's headed for the doctor tomorrow night, so they can do a fuel pressure test and diagnosis on friday. I'll keep you posted.

Leland Pate · 01-30-2002, 07:46 PM

My car has always done that.
The colder it is, the harder it is to start... it just stumbles very hard...usually take like three tries then it fires just fine....but then it idles at like 2200 rpm for about 30 seconds...then it slowly steps down.
I thought I had a bad WUR/thermotime switch...so when I rebuilt...I replaced 'em all.
Guess what... it's still doing it.

I give up.

wckrause · wckrause's Garage

I used to have that same problem. Took it to two different mechanics who tried swapping different components. Neither of them had any luck fixing it. They both blamed it on vacuum leaks caused by age, and said it couldn't be fixed unless they pulled the CIS and replaced all of the seals, hoses, intake runners etc.

I lived with the problem for a long time until I found this board. I bought a CIS tester, the Probst Bosch Fuel Injection book, and spent a couple of long weekends going over the whole system, piece by piece.

In the end, a couple of knocks with a hammer (to adjust the WUR), and a couple of squirts of Gumout through the thermovalve, solved all of my problems. Total cost was under $100. My car now starts to a smooth idle first time, at temps close to 20 below zero.

CIS can work, and it's really not that complicated.

(BTW, rough running at cold start is due to being too lean. JW is dead on).