Idle speed

  • Hello to the round,


    the engine of my 87 turbo has a strange behavior right now.

    Idle speed at about 700.


    While driving everything is ok.

    Only when shifting the speed drops to about 200-300.

    Sometimes the engine is about to stop.


    Does anyone know the problem and can help me?

    I do not want to start to put on any screws, since the problem was not a week ago.


    Thanks in advance :B

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    911, Bj. 7/1987, 3.2 l

    911, Bj. 7/1987, 3.3 turbo

  • Hello Ralf,


    your signature says 3.2l, that would be a Carrera and no turbo, will probably be a typo!?!!

    Turbo is the G model afaik always normal K-Jetronic (so purely mechanical and without lambda control). I do not know the Turbo from my own experience, only my US SC. But I have completely tested the K(A)-jetronic.


    The phenomenon occurred suddenly, right? Do you screw it yourself?


    With the K(A/E)-Jetronic, the main disturbance factors are mainly false air and other problems that negatively affect the mixture. Now, if the RPM is lower at idle and it almost stalls when changing gears, in all likelihood the mixture is too lean due to false air. Therefore, my first measure would be to check for false air. Therefore, the complete intake manifold including the injection system with a smoke generator from the flow divider to check for false air, if necessary, also with some overpressure. Tests with brake cleaner or only cigarette smoke do not lead to the goal! As a cross check, a lambda measurement at the exhaust would be advisable to see if it is really too lean at idle.


    Greetings, Thomas

    This post has been automatically translated.

    81er ex-US 911 SC Coupé, platinmet., eSSD, K-Leder sw., Turboheckflügel & -frontspoiler, NSW, Maxilite 7/8J, Bilstein Fw("SpoStra" - noch...), 915/61, 930/16 o.Kat, WebCam 20/21 NW, hydr.KS, Dansk 92.502SD, 123 Ignition, orig. Porsche SWV, Seine Systems Gate Shift Kit, Momo Prototipo m.Nabenerhöhung


    „Nicht das Auto verdirbt den Charakter, aber wer keinen Charakter hat, sollte nicht Auto fahren.“

    Ferdinand Porsche

  • Hello Thomas,


    my signature is not quite correct.

    I have the following vehicles:


    3.2 Carrera from 7/1987 and a

    3.3 turbo from 7/1987


    The problem actually occurs with the turbo.

    The 3.2 runs great.


    I already screw myself up to a certain point.

    Had also already times engine/gearbox out.

    But with electronics is slowly end :(


    I have read a lot here.

    With the false air is certainly a possibility.

    Since the car had an engine overhaul only about 1500 km ago.


    I remember driving a bit "brisker/sportier" at times before the problem occurred.

    This could of course have been the trigger for a "leak"?


    But is also only a guess

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    911, Bj. 7/1987, 3.2 l

    911, Bj. 7/1987, 3.3 turbo

  • But with electronics is slowly end

    The K-jetronic of the turbo has wimre no electronics, but only a little electrical (WLR, ZLS and fuel pump relay). So still a proverbial purely mechanical injection system. But has m.M. currently nothing to do with the current problem, as long as cold start, idle and general drivability until the appearance of the problem have been completely I.O..


    Therefore, the question again: Has it suddenly occurred?


    My advice: Find a workshop and borrow a smoke generator or get one yourself (always a very good investment with a K-.jetronic!), and put the injection system and all air leading hoses from the flow divider under smoke and see if smoke comes out somewhere where it normally should not come out. I bet that there is at least one leak. It may not be so noticeable under load, but it is when the engine is idling and the throttle is released.


    Of course it can be something else, but false air is the most obvious. I've already written about it here in PFF, which concerns only the SCs and Carreras, but here as there on the turbo, the troubleshooting is similar. I also mentioned there the smoke generator that I use. We had on the subject of false air in the last several threads here. So that one does not accuse me here in the PPF of advertising, I do not put the link to the device here any more, but refer to the search results:

    https://www.pff.de/wcf/search-…776/?highlight=falschluft

    In the corresponding threads you will also find links to documentation and videos that deal with the K-Jetronic (called CIS in English).


    As long as false air cannot be 100% excluded, it makes no sense to look for other errors. (None!) False air is beside clean (gasoline) pressures with the K-Jetronic there A & O and at the same time the largest enemy!


    If you want to read up on K.jetronic first - I have linked some literature elsewhere, but it all refers to non-turbos, but should not be a problem, since the basics are identical for both:


    Greetings, Thomas

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    81er ex-US 911 SC Coupé, platinmet., eSSD, K-Leder sw., Turboheckflügel & -frontspoiler, NSW, Maxilite 7/8J, Bilstein Fw("SpoStra" - noch...), 915/61, 930/16 o.Kat, WebCam 20/21 NW, hydr.KS, Dansk 92.502SD, 123 Ignition, orig. Porsche SWV, Seine Systems Gate Shift Kit, Momo Prototipo m.Nabenerhöhung


    „Nicht das Auto verdirbt den Charakter, aber wer keinen Charakter hat, sollte nicht Auto fahren.“

    Ferdinand Porsche

    Edited 2 times, last by Schulisco ().

  • Thank you Thomas.

    I will read up on all this.

    The smoke generator is a very interesting thing.


    Thanks again 👍

    This post has been automatically translated.

    911, Bj. 7/1987, 3.2 l

    911, Bj. 7/1987, 3.3 turbo

  • The smoke generator is a very interesting thing.

    Exemplary this thread, there I wrote down how I searched and finally found one of the main problems at my SC (the whole thread is also worth reading):


    Greetings, Thomas

    This post has been automatically translated.

    81er ex-US 911 SC Coupé, platinmet., eSSD, K-Leder sw., Turboheckflügel & -frontspoiler, NSW, Maxilite 7/8J, Bilstein Fw("SpoStra" - noch...), 915/61, 930/16 o.Kat, WebCam 20/21 NW, hydr.KS, Dansk 92.502SD, 123 Ignition, orig. Porsche SWV, Seine Systems Gate Shift Kit, Momo Prototipo m.Nabenerhöhung


    „Nicht das Auto verdirbt den Charakter, aber wer keinen Charakter hat, sollte nicht Auto fahren.“

    Ferdinand Porsche

  • The reason for a drop in speed when shifting can also be a too rich mixture.

    Don't know how it is with the turbo, but with the SC a faulty vacuum line to the WLR could trigger the described effect.

    If the vacuum at the WLR is missing, e.g. due to a defective thermo valve, the full load enrichment is permanently active. Under load, this is not necessarily noticeable, but at idle speed, the engine almost dies.

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  • The reason for a drop in speed when shifting can also be a too rich mixture.

    Don't know how it is with the turbo, but with the SC a faulty vacuum line to the WLR could trigger the described effect.

    If the vacuum at the WLR is missing, e.g. due to a defective thermo valve, the full load enrichment is permanently active. Under load this is not necessarily noticeable, but at idle the engine almost dies.

    Mhmm, not quite... The air, which goes through the air intake valve, the auxiliary air valve and the start valve, is not really false air, because it is only branched off behind the air dam (on the SC, this angled piece of aluminum pipe on the back of the rubber cover). Thus, this air has already been "measured" through the baffle plate.


    However, it is also true that this air is "too much" for the moment when one of these valves is permanently open, i.e. it will then actually continue to lean. But the effect can be exactly the same. This is what makes troubleshooting a K-Jetronic car so complicated and sometimes confusing.


    Greetings Thomas

    This post has been automatically translated.

    81er ex-US 911 SC Coupé, platinmet., eSSD, K-Leder sw., Turboheckflügel & -frontspoiler, NSW, Maxilite 7/8J, Bilstein Fw("SpoStra" - noch...), 915/61, 930/16 o.Kat, WebCam 20/21 NW, hydr.KS, Dansk 92.502SD, 123 Ignition, orig. Porsche SWV, Seine Systems Gate Shift Kit, Momo Prototipo m.Nabenerhöhung


    „Nicht das Auto verdirbt den Charakter, aber wer keinen Charakter hat, sollte nicht Auto fahren.“

    Ferdinand Porsche

  • Thomas, I mean the electrically operated valve in the vacuum line to the WLR. This is closed without current, is energized together with the bimetal of the WLR, and normally opens approx. 20 seconds after starting.

    If the valve is not energized, the vacuum line is closed and thus the full load enrichment is permanently active. This results in approximately the behavior described above. Lambda at idle sometimes briefly at 0.7. Engine sometimes shortly before stalling, but usually recovers.

    Guess how I know this - I damaged the cable while tinkering. :(

    Greetings Peter

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  • Oh, you mean the "911 606 106 01" on the RdW...hmm, yes, but its air supply is also behind the pressure plate. Whereas - you're right: If that would be permanently open, then the mixture would still indeed too rich, because the vacuum in the WLR reduces the control pressure and thus then greases the mixture. The turbo (930.66) doesn't have this valve, but something similar near the ZLS (928 606 215 01 electro air valve).


    Greetings, Thomas

    This post has been automatically translated.

    81er ex-US 911 SC Coupé, platinmet., eSSD, K-Leder sw., Turboheckflügel & -frontspoiler, NSW, Maxilite 7/8J, Bilstein Fw("SpoStra" - noch...), 915/61, 930/16 o.Kat, WebCam 20/21 NW, hydr.KS, Dansk 92.502SD, 123 Ignition, orig. Porsche SWV, Seine Systems Gate Shift Kit, Momo Prototipo m.Nabenerhöhung


    „Nicht das Auto verdirbt den Charakter, aber wer keinen Charakter hat, sollte nicht Auto fahren.“

    Ferdinand Porsche