Idle hunting?
 

Guys I have an 87 911 which is idle hunting from 500 - 1100 rpms.
The car does this whether its hot or cold. I have performed a search on this issue, and there is indeed a bevy of posts regarding this issue, and a multitude of items to check to identify and rectify, but in no logical sequence. Yeah, I'm basically a newbie...
Can anyone post a logical sequence of avenues to pursue to rectify the problem?
Thanks so much in advance for your expertise...
Paul:D

Idle Control Valve. ICV...

I have same problem. Will go to opc to conect it to pc. It could be icv, o2, untight mainfold, idle sensor....

As a911 stated...Start with the following:

Check the ICV...With the engine off, turn the key to the on position. You should hear/feel the ICV buzzing. (good thing)

Take the ICV out and clean it with carb cleaner. The innards of the valve should turn freely. You'll see what I mean once you take it off.

When was the last time the 02 sensor was replaced? Over 30K miles ago?

Run some techron injection cleaner through a tank of gas.

Torque the manifold bolts, all 12 of them to 18 ft/lbs.

Check all the hoses and vac. lines for possible leaks.

Re-set your idle.

My thoughts are: When the car is experiencing a STEADY and significant up and down idle, it's likely the ICV.

Vacuum Leak

Thank you gentlemen...I will follow your process of elimination.
A porsche wrench I talked with, said that maybe I should first start with adjusting the idle control screw (6 or 7mm) adjusting screw. Does this sound valid?
Regards,
Paul

That would be last thing on my list

try adjusting the idle speed down to 850. a too high or too low idle speed will cause the surging. be sure the micro-switch on the throttle housing is functioning when the throttle is closed. check at it's plug with an ohmmeter while you open and close the throttle.

How about step by step w/ some pic's?

To set your idle:

On the drivers side of the engine compartment you have a black plastic cover.

Take it off and you'll see a black plug with 5 female sockets.

Start your car and bring it up to operating temp.

The black plug with the 5 sockets located at 9, 11, 2, 3 and 6 o'clock.

You jump (bridge) a jack (jumper wire) between 2 and 6 o'clock.

Set your idle from the throttle housing screw.

hope this helps.

Reading a lot of post on the subject seems that when i jump 2 and 6 oclock which some refer by letter. The idle would go to 880 and be rock soilid, at that point which way sould i turn the screw and will my idle change at the time of ajustment? or is it hit or miss by turning screw remove jumper see results, so on and so on. Idle at cold start is 1200 for 1 min. or 2 and settling down to 700, when full warm it will go as low as 500 and fluctuate to 700 at idle after 4 or five min. slow decrease and increase. The idle sounds so much better when it reads 700 +/- 20rpm on the tack. It stays steady at 500, then a small stumble and the rpm will rise to 700 for a min. and slowly go down to 500 sit for a couple of min. and repeat its self.

Cold start at 20F sitting for weeks 3 to 4 seconds crank time and she fires right up, stays soild at 1200.
87 with 179,000

Setting the idle correctly will not necessarily cure your problem but it is just one of the easiest/first steps to perform in the diagnosis. You are getting that engine up to operating temp. before attempting to set the idle, right?

Note: Jumping the plug only serves to bypass the ICV when setting the idle.

Refer to the earlier post for additional checks to perform. ICV, vac. hoses, 02 sens. (last time it was replaced), air filter, etc.

There are many steps to work through prior to just replacing parts and having a shop set your fuel mixture.

You mentioned it sat for a few weeks in very cold weather. How did it run prior to having the car sit? One of the first thing I would do is get it out for a sprited run once it's at operating temps.

With the engine at normal operating temperature, insert the jumper as described. The idle should be set set to 850 +/- 40 rpm's. Remove jumper. I belive this should properly set the idle; if I am understanding KQW's directions.
Hopefully, one of the more technically adept can chime in and verify this procedure.

Advise how deep you are capable of getting into the the diagnosis of the Carrera.

Setting the idle correctly will allow you move on to next steps. On the Carrera 3.2, you can move pretty easily through steps and procedures prior to making a trip to your Technician.

Please note: Setting the idle is one step and if the issue is not solved, then go to next steps like the vacuum, ICV cleaning, CHT checking, manifold bolts, manifold boot, breather restrictor valve, pressure valves, injectors, valve clearance, etc.

After checking the above, you'll probable need to go back and re-set the idle.

Do a search, I believe that Indigowhale went through a similar issue and you will see a myriad of info and steps.

kqw, thanks for sequencing.

No problem Nine...

I've owned my Carrera since '86 and other P'cars since '74. By far the Carrera was the easiest/fun to work on.

Do you have Wayne's 101 or the Bentley Manual? These books will assist greatly in understanding the car and DIY procedures.

Kqw, thanks for the input.
I jumped the ICV and she steady at 850 +/- 20. as i turn the nut the screw also turns (is that normal?) or should i hold the screw and back nut off, then turn screw left or right to raise idle? then tighten nut down.
I have replaced:
Cap and Roter(needed it bad)
CHT(fixed cutting out and poor start, and was singel wire)
O2(had no idea of age)
DME relay (new one is solid state)
Pipeline (goes to throttle boot, the ruber end was dry rot with large crack, im sure it was drawing air)
Inspected all vaccume lines, replaced reducer that holds restrictor valve
Conected vac. hose from thermal valve to ambient air valve was not there and appears that it should be.
All this was needed and now I'm just want to fine tune the idle.
I have not changed the spark plugs or tightend down intake manifolds.

I followed kqw's instruction to set the idle, and with the plug jumped the idle did not change with one full turn in either direction. Does this indicate the ICV is bad?
I turned the key to position one and could not hear/feel the ICV buzzing.

Hello Nine

It's the "on" position..i.e., last click before cranking the engine.

Try it again...

Thanks

Ahhh, thats better. I can feel the ICV buzzing. Could the valve still be bad, or does this indicate that the problem lies elsewhere? ie vacuum leak, o2 sensor, manifold leak...