porschesctarga

My 911 normally idles between 9 and 10k RPMs. At times, mostly when it has not yet warmed up, it seems to be searching for idle. It swings wildly between 3 and 12k RPMs and eventually stalls. It is inconsistant. As times it warms up just fine. Other times it just will not idle smoothly and eventually dies every time I slow down to stop or even engage the clutch. I am wearing out the starter. Any help in diagnosing and fixing this problem whould be much appreciated!

Steve Wilwerding

First off, I'm pretty sure you don't mean that it idles between 9K and 10K, since those are both way over redline - you proabably mean 900 - 1000. Also, I'm hoping that it doesn't go up to 12K when "searching for idle".

Matt Chamblin

Sounds like you possibly have a bad W.U.R. or yours is out of calibration. The only way to check is with a fuel system pressure test.

Where are you in Nor-Cal?

john walkers workshop

first set the CO when the engine is hot to 3-3.5% on a exhaust machine, then see how the cold running is after that.

pbs911

Mine did hte same thing. I followed JW's advise and the idle is now rock steady. You can pick up a Gunsten emissions analyzer for about $125, which worked fine for me.

an6drew

My '82SC also hunts for idle, pulsing within about a 100rpm range though. Idle speed has also dropped recently- 2 weeks ago it was idling around 750 +/- & now it seems to be in the range of 500-600rpm! I was planning an ignition tune-up this weekend & a bit of a play with the idle adjustment screw. Sounds like I'd need to get it on an emissions analyzer @ the same time???

porschesctarga

Yes, I meant it normally idles between 900-1000 RPMs.

The engine stalled out at every stop light this morning. It is definitely getting worse.

What is the "CO"? I do not have an exhaust machine so I suppose this means a trip to my machinic to set the CO when the engine is hot to 3-3.5% on a exhaust machine and / or a a Gunsten emissions analyzer?

I am in the East Bay area of CA.

porschesctarga

Fist, thanks for all you help! I did some seaching on the topic and got some answers. (Sorry - I am a rookie / newbie and new to Porsche 911 ownership world - obviously a lot to learn but I am having fun with it.

WUR - Warm Up Requlator

I have not checked yet but if my 78 SC has the AAV still connected should I disconnect it? I read in a previous post:

"After twenty years there shouldn't be a single SC around with the AAV still connected."

Could this be part of the problem if I do have it still connected?

Also, in this thread and other posts on this topic it is suggested:

"You must set the CO level with a meter. If you don’t have a O2 sensor set the CIS at the rich (high CO) level. My CIS system is quite sensitive to adjustment so "playing" with it will soon have you in trouble."

I don't have an O2 sensor. Any advice on how to adjust with out one or would you reccomend getting one to adjust the CIS? BTW: what CO?

Hladun1

I said disconnect the AAV (not AAR) and I still mean it. Disconnecting the AAV also stops startup backfires. Also, make sure the deceleration valve is properly set.

porschesctarga

I apologize, I misquoted you. I will disconnect the AAV. No problems with startup backfires. Just the hunting idle problem. I read your previous posts and will use your advice this weekend when I try to work out this problem. I will do some research to learn how to make sure the deceleration valve is properly set.

This is the first problem I have had with my 78 SC. I have had it for just over a year. It is at 190,000 miles.

As soon as I bought it, based on research I did on Rennlist and Pelican Parts, I made these upgrades:

installed a pop-off valve, chain tensioners, steel brakelines, alternator with a built-in voltage regulator,

and due to some engine oil leaks, engine re-sealed. Also a valve job, new plugs and wires...etc a major tune-up.

I love my 911!

Thanks again.

Hladun1

Sorry to sound abrupt about the AAV, I didn't mean to be. Good luck fixing your problem.

spankyone

I had the same problem on my '82 911SC. Turns out that the O2 sensor wire had fallen off. I tried everything!! Mixture, timing, plugs, rotor and cap, new O2 sensor, etc. Turns out that the O2 sensor is critical in maintaining proper fuel mixture levels. Once I fixed the wire (very easy by the way to fix/replace O2 sensor) the car runs like a champ. Idles strong and steady at all temps, no hesitations, more power, better starting. Someone else had told me to run a high mixture as well, i.e. 3%, but when I thought about it, the O2 sensor is still going to be critical in maintaining any mixture level. I hope this helps...

dial911

Yes, but this thread was originally about a 1978 3.0 SC.
The '78 did not have a O2 sensor.