Idle issues
 

This is how my sc is currently behaving at start-up.

It starts fine ( from cold) and idles alright. It fluctuates a bit but it idles, and revs quite nicely.

I can drive away and after it warms a bit it starts to not idle ( this is before it is fully warmed)


My experience so far is that once fully warmed it'll idle properly and drive nicely although because of it's refusal to idle while getting up to temperature I've been reluctant to take it in traffic, therefore I can't 100% guaranty the above statement.


I suppose I could try to get it completely up to temperature by idling in my driveway but I can't imagine how long that might take or if it's even possible.
Are there any suggestions as to what I might look at to correct the idle problem?

Thx
Hugh

A fundamental approach is is best. No particular order except maybe a bias towards false air detection.

Eliminate vacuum leaks.
Check you ignition timing.
Check the inside of the dist cap for deposits on the rotor tip and contact points
Pressure gauges for checking fuel pressures
CO meter for AF ratio. You can cheat and use an analog dwell meter.
Check Aux Air Regulator function with a mirror on a stick before and after warm up.
Do the squeeze procedure on your aux air valve to seal off a tired diaphragm. Alternatively, stick a golf tee in the small hose that sucks on the diaphragm unit.
Take your other golf tee and stick it in the retard hose going to the vacuum/retard pod on the side of the distributor. It will be the hose that has vacuum on it when at idle. The vacuum advance hose does not "suck" until off idle.

The last procedure masks inefficiencies from an aging CIS system. It bumps dist advance up about 8 degrees but only at idle. Try that first. It's simple and you may be surprised at the liveliness of the car at idle. If it revs up to 1500 plus when first started and hangs there before dropping, it's normal.

Listen to the other guys. e.g., T77, boyt911sc.

Before we get too technical, how much mechanical experience do you have? In other words, is this your first 911?

Cheers,
Joe

You may want to have a look at my thread, as I have similar issues

http://forums.pelicanparts.com/porsche-911-technical-forum/1006856-revisiting-issue.html

Jason

It is my first 911 and on a scale of 0 to10, my mechanical experience might be 3 or 4.

Oil and filter changes, some brake work and very light electrical work. Zero knowledge of the workings of CIS. I either have to try and learn or find someone that understands the system (my preference).


Hugh

good time to learn to heel and toe:)

did you buy it like this or as it running fine then started doing this

Ha Ha, Good point. Heel and toe would be nice but I think I would prefer the CIS system would work as designed.

Yes, the vehicle appeared to be running fine this summer as I had two 600 to 800 mi week-end trips. Half way thru the second week-end trip I did start to have inconsistent idling problems and since I've been home it seems to have gotten progressively worse.


Hugh

you need to post the year

Techron first, Then vacuum leak checks. I fixed my idle problems by fixing intake runner leaks .

"you need to post the year"...………"83

"Techron first, Then vacuum leak checks. I fixed my idle problems by fixing intake runner leaks ."

I've heard nice things about Techron and I'm sure it's worth a try. The intake runners are all new since this spring. The air box was also replaced at that time.

"Start with the basics.

Monitor your fuel pressures on warmup. '


A good suggestion. I'll get the pressure gauges hooked up and monitor the pressure as the engine warms up...….if it'll keep idling while it's warming.

techron is good stuff, but for it to work you have to drive it. I prefer a bottle to about 1/2 tank, maybe less. then I like to keep the RPMs up. 4-5k. like slowy accelerate but run it up in RPM. between stop lights run it up in RPM and just hold it. you need to get lots of fuel flowing thru the injectors.

it really sounds like a mixture problem to me.
I assume you don't have fuel gauges.
I would look at the inlet screen to the warm up regulator. make sure it is clean.
make sure you have good power to the WUR.
check fuse 18.

remove the air filter. lift up and pull down on the air flow sensor arm to see if it will idle. you can do this as it warms up.

Thanks to Tony (boyt911sc) I've replaced the WUR with a recalibrated unit that also has the adjustment screw added into it.


The car is running much better although it has died a few times when stopping for a red light, but I don't think it's related to the WUR. Maybe it has something to do with an air leak.


I'll try to find time to do more checking in that area.

Thanks to those that took the time to reply.

Hughc

Unmetered air.........
 

Hugh,

You need to test and confirm the absence of sources of unmetered air. Search for EVAP smoke detector in the Internet. It cost less than a $100 to have a nice smoke detector or build one. Not until you have pressurized and tested the system would I agree with you that there is no significant source of air leak. Not being able to find it does not mean you don’t have any.

After you had passed the pressure test, have the exhaust analyzed using a gas analyzer. Keep us posted.

Tony

Start with the basics. Make sure your aux air regulator (AAR) has power getting to it. The way you describe the symptoms point to it not being connected electrically.

Just an update.
Since my last post I decided to send the distributor out for a complete rebuild. The rebuilder said "this distributor should have been rebuilt many, many miles ago".
There was much snow on the ground when I got the distributor so I wasn't able to go for a test drive, but after installing it I found the engine started and idled very smoothly
I hadn't put a timing light on it and the idle was a little high at 1400rom but I was able to drop the rpm with a slight adjustment to the distributor .

I decided to drop the engine, for several reasons.
1- to check out the work I did when I removed the cis system last spring with a partial engine drop. It was quite difficult doing that work with a partial engine drop and I was never quite convinced that everything was as it should be. Thus In one of my other post i had questions concerning the small vacuum lines.
2- I wanted to do a valve adjustment and figured it would be a lot simpler with the engine on a stand
3- I wanted to check for the source of oil leakage on passengers side cyl 6. I'll know a little better once I can have a closer look at it
4- perfect opportunity to have a look at the clutch (95K mi).
5- I also intend on cleaning the engine without getting too anal about it.

So the engine is currently on the floor and the transmission is separated. I'll be replacing the clutch and god knows what else. I think the flywheel and pressure plate are good to re-use.
I think I may have embarked on that slippery slope.
Rather then put the engine on a proper stand we are trying to devise a way a way to get it up and supported so that everything is accessible

The engine tin has been removed and, well, the slippery slope took over.
The tin was sent out to be blasted and powder coated and it looks beautiful.

We've decided to remove the cis system completely so there's no possibility of damage when we pick it up (with the crane).

Now I can see where the cooling cowl is in bad need of new paint. How do you guys deal with painting this piece?

So, this job is going to take longer than anticipated but hopefully I won't screw up and have it finished in time for the warmer weather.

Awesome we need some pics! :).

I'd like to post pics but I haven't had much luck doing that.
The site won't take pics from my phone and I haven't sorted out the lap top thing either.
Unfortunately this pic thing isn't much of a priority thing for me at the moment since I think I'll have my hands full with the work I'm attempting. Sorry.
I do have some photos on my phone and maybe some day they'll get posted.
Not to be obtuse, but there have been lots of engine drop photos on the forum and I'm sure most are more appealing than my job.

I'm just really concerned now with what clutch parts should be replaced and what can be re-used.
Should be interesting.