1988 911 Idle undershoots and cuts out

[Mike Young]

Hi

I've just bought a 1988 911 Carrera 2 Targa 3.2L. The car starts every time and idles smoothly at about 900rpm, BUT when you are driving the car and take you foot off the throttle, for example when approaching a junction, the engine speed undershoots the idle speed - sometimes cutting out and sometimes it just manages to catch itself and returns to a steady idle.

It does this when the engine is cold and when its hot.

Thanks in advance for any suggestions.

Mike




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[adam s]

Mike

Mine does it when cold, but its okay once warm. I've read that quite a few cars seem to run the same, and aside from checking the electrical connections, it seems to be something to live with. If yours is suffering most of the time it could be an idle management/mixture problem, and is well worth a trip to a specialist.

Sorry I can't help more.


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[Decolliber]

You need to adjust the idle. It is a screw on the intake (7mm hex as I recall), and should have a plastic cover over it. I think clockwise raises the idle, but I have not done it for a while. But first you need to bridge two points on the pins under the cover on the left hand side of the engine compartment (the two pins at 1 o'clock and 7 o'clock). Then adjust the idle so that it does not change when you remove the bridge. You can easily do this yourself. I had the same problem on my 1988 Carrera, and it is easily fixed; you do not need to live with it.

Ideally you should have the mixture adjusted first, which requires an exhaust gas analyser. Some mechanics will tell you that they can adjust your mixture ny putting a voltmeter on the O2 sensor, and adjusting mixture until you get rapid fluctuation around 0.8V, but this is unreliable. One mechanic made my mixture far too rich doing it that way, and left me with a surging idle, a classic symptom of excessive richness.

If you want to do this and need more details send me a message and I will dig out my references for you. The topic is dealt with on the 911 tech bulletin board at pelicanparts.com; just do a search on "idle" or something like that.


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[Mike Young]

John

Your smack on mate !

I've just got it sorted exactly as you said. Just wish I'd read this response a few weeks ago.

Thanks

Mike




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