'85 idle problems

[Silver 911]

Can anyone help? I just purchased my first Porsche, a 1985, 911 with 90k miles. My problem lies with the cars idle which is very rough. I was told it might be my O2-Sensor, can this be the probelm, and if so, can I replace it myself.
Thanks in advance.

[Joeaksa]

Silver (what is your real name, we are a close group here),

Welcome to the forum!

Look in the upper right side of the screen and you will find the search button. Hit it and in the upper left hand window on the new screen you will be able to type in "idle" and something like "DME" or "3.2". Make sure that in the lower window on the left side you specify "911 tech forum" otherwise it will give you hits for all the cars.

Now, about your idle. Rough could be several things. Is it stable, hunting up and down or so on. Does the car die from time to time or? Also, update your profile with where you live. Many times its something that occurs in your area, like Oregon and the rain can give fits to DME cars due to the water in the distributor and so on...

My car is like yours, another 85 and has had various idle problems. One is the idle stabilizator valve, other items that can cause problems are the oxygen sensor and the cylinder head temp sensor.

Some things to be aware of here are that your car is a Carrera and the fuel injection is different from the earlier or later cars. Systems like yours are in cars from 84 until 89 and are referred as "DME" cars as they have the digital motronic electronic fuel injection systems...

I just did a search for you and came up with over 40 replies. The below url is typical of what you will find. 3.2 idle question

Hope this helps and post more info so that we can help figure out the problem.

Joe

[Silver 911]

Thanks Joe, glad to be at the forum. This is my first try..so all... be patient. PS will post name and fill in profile.
Thanks again.

[Joeaksa]

More info on the problem and when it occurs is better. Cold, hot, both, and have you had the car tuned up and looked at by someone who knows 911's? How many miles and so on...

Also, posting the area helps as there might be another person on the forum who can help. I live in Phoenix and we trade parts and help all the time.

Joe

[Silver 911]

The car has 90k on it and the rough idle occurs all the time. I had a Porsche mechanic do a pre-purchase inspection and he was the one that said it could be the O2-sensor. The car was tuned-up about 2000 miles or so and that was about a year ago, according to the car's records. The car never stalled, but taking off in first, there's some hesitation. Also, when I check the oil the idling gets even rougher but again, never stalled. I live in NYC.

[DJB]

Is your oil filler cap properly fitted. If it is not on correctly or missing - this will lead to a very rough idle at th very least.

[Joeaksa]

Do you have the maintenance records from the previous owner? 90k is about the limit on a oxygen sensor and would be nice to know if its been replaced. You can replace them yourself if you are a bit mechanical. Its located on the exhaust pipe under the left rear wheel well. Look for something that looks like a sparkplug screwed into the exhaust pipe with wires attached. Pelican sells them and I would get a "Bentley" tech manual as well.

Dave is correct about the cap. Have you checked all the vacuum hoses around the motor compartment? Several there and they can cause idle problems. How far are you from Long Island? Some good people over there and there was a thread in the last week with several people helping a new owner on LI with various issues on his car.

I had my car stutter on takeoff and could not find it. Took it to a shop and they scoped it and the distributor cap was cracked on the back side. Fixed it in 30 minutes and drives fine now...

One issue with cars that have not been driven much is white foam on the oil cap. If you do not drive the car long enough to let the oil get to operating temp you can get a white foamy deposit on the oil cap. Take the car out and drive it, get it warm and go on the highway for a bit. Then check the oil again and it should go away...

911's are different but once you get to know them there's no substitute!

Joe

[carreradpt]

Also, Silver it is normal for the car to idle rough when the oil cap is removed to check the oil. Though it should smooth out when the cap is replaced.

[Siena911]

Mine had a rough idle which was a leaky inlet manifold gasket. Spray some carb cleaner around the inlet manifolds where they join the head and if she settles down, you have found the leak.

Drove me nuts till I found it, all of £3 to fix.

Cheers Jakes, and welcome to the board

[ChrisBennet]

Originally posted by Silver 911
Thanks Joe, glad to be at the forum. This is my first try..so all... be patient. PS will post name and fill in profile.
Thanks again.
--> Your name here <--

Just teasing ya. Welcome to the group.
-Chris

[CrossT]

Welcome to the group Silver.

You'll find some helpful people here. Some are quite knowledgeable. I'm new, so have been the beneficiary of others' knowledge on the DME system. I have tuned my 86 to solve irregularity in the idle as well as flat spot in the 2500-3000 range. It was the O2 sensor in my case, though I replaced other potential items as well to include the wires, plugs, dist cap, rotor, head temp sensor. Then had local service guy scope a fine-adjust. Runs well now with the exception of occaisional oscillating idle which I am planning on addressing before I return to work after the 1st. Anyway, the O2 sensor is a common suspect on these and if you don't know the PO's last replacement (if it ever was), it might be a good place to start.

welcome again,
todd
--------------------------------
86 cpe

[Joeaksa]

Todd brings up a good point. The oxy sensor is not hard to replace nor very expensive. Pelican has them as well as some people on the forum have replaced theirs with generic Bosch units and adapting the wiring. Just depends on if you want to tinker a bit or have it plug right in.

Joe

[Silver 911]

I have found the sensor, but do I have to remove the wheel to get at it? Also, the head thats goes to the exhaust pipe, does it screw or pull out?

Art

[Joeaksa]

Art,

Not sure which sensor you are talking about. If you are talking about the cylinder head temp sensor, then its best to jack the car up, put it on jackstands, then pull the wheel to get some working room. Its a bear to get to and work on.

Before you do this, are you sure its a old type cyl head temp sensor. Go inside the motor compartment and find the three connector rail on the left side below the heater motor. Top plug on my car was the cyl head sensor. Feel on the wiring coming and going to the motor and if both sides has two wires, then you have the new style. One wire on one side and two on the other side means that you have the old style and need to replace it, even if its not bad... it will go bad and at the worst possible time.

You mention the "head that goes to the exhaust pipe" and this is the oxygen sensor that screws in the left exhaust pipe. Two different animals... This one has a heat shield that clips to the sensor (normally there) and just pull it off. Then you will see a "sparkplug like" sensor that just screws into the exhaust pipe. You might have to heat it up a bit to get it moving, and if you have a flare nut wrench it might be better than a normal open end.

Joe

[stlrj]

A bad 02 sensor would cause the fuel injection to default to rich which would make the engine idle smoother. Therefore, I would look somewhere else for your rough idle problem like clogged injectors, intake manifold gasket leaks, bad plugs or ignition cables/connectors etc.


Regards,

Joe