Smooth Idling

[moosthuizen]

I'm a first time porsche owner, I own a 911sc 1980 model, got it 3 months ago. It has 150 k kilometers on the clock. I've replaced all the vacuum hoses, installed new Bosch plugs, new distributor cap and put in new plug leads.

The problem is not so much with irregular idling. When driving it is as if it is not performing as it should. I wont say its jerking, but thats the closest I can get to axplaining what it does.

I think the same problem manifests itself in the idling. It does not idle to bad, but is not constant or smooth. After I've turned the adjusting screw between the airbox and injectors, to the right, it improved, but still does not idle smoothly. Cold start: starts immediately, idles at 6000rpm andafter a minute or so when hot goes to 9000rpm. No problems with warm starting.

Ive set the timing at 5 BTC, also tried at 8 and 3, no improvement. It is actualy quite economical on fuel, and exhaust always burns white grey(I use leaded gas)

Any suggestions?

Marius Oosthuizen
Johannesburg SA
911 sc '80

[SpeedracerIndy]

Idles at 6000 and then 9000 RPM!!!! I hope you mean 600 and 900 rpm. If it's jerking or bucking while driving it sounds like a vacuum leak. If you do a search on vacuum leaks you will find lots of info on how to track one down.

[moosthuizen]

Yip, meant 600 to 900 rpm


Marius

[jdowty3]

I think the O2 sensor can cause a similar symptom but if yours is a Euro, I don't think it has an O2 sensor. I don't remember if the problem occurs when the sensor is connected or disconnected but many have posted threads about similar surging issues.

[moosthuizen]

Hi Jim

I'm not sure if mine is a Euro model or not. How do I tell the difference? Mine do not have any emmision cotroll stuff, if that helps. It's a left hand drive, over here the cars are right hand, so this might mean Euro model.

Marius
911 sc

[porschenut]

If you have side marker lights and no emission control equipment, then yours is a Euro model.

[targa80]

I believe that when the car is cold and started the idle should go up to 1600~1800 RPM and drop down to 950 RPM as the engine warms up. So if you idle is at 600 RPM at startup I would think that is a problem to start with.

[Jdub]

What is the CO set at? Try 3.5%.

Baseline the car. Replace oil, gas filter, air filter and take a look in the airbox and oil blowby pipe for any old oil. Clean the sensor plate (carefully) in the airbox while you are in there.

Try removing the oil cap and see if the idle falls - it should. If it does not, chances are you have a vacuum leak.

John

[SpeedracerIndy]

The best way to tell would be to look at the engine type which is on the right side of the cooling fan. I don't know what type engine an 80 RoW has though.

[fintstone]

If you are adjusting your air/fuel mixture to set your idle, that is probably your problem. You must use some sort of exhaust analyzer to do this properly. I would suspect that you are probably too lean based on your plugs info (not black and sooty=too rich).

[moosthuizen]

Thanks for all the info, I'll see if i can get it properly set with axhaust analyzer. By the way mine has side indicators, I'm sure it's an Euro model.

MO
80 911 SC