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Thread: No throttle response. 2.5 X type

  1. #1
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    No throttle response. 2.5 X type

    Hello all,

    A rather strange problem, I have just replaced the head gaskets but had a problem after with misfire codes on 1,3 and 5. after checking it seemed likely I had mistimed the cams on that bank. That corrected on restart if started normally, idling at about 1100 for a few seconds then droppd to about 750, as it used to do. after a couple of minutes or so I revved the engine to over 5000 rpm which it did with no problem. (With the mistimed cam this would bring the engine check light on and the misfire codes.) On releasing the throttle the enggine dropped back below normal idle then stalled. It restarted straight away but idled at only 500 or so rpm and does not respond to the throttle at all. The engine check light lit and came back with a code of P0128, which is the slow arm up warning, which seemed irrelevant to my problem. No other fault codes.
    Does anyone have any experience of such a problem? As it seemed rather odd I have disconnected the battery to reset the ECU but any suggestions of what else to check are welcome?

    Alec
    2004 2.5 X Type Estate, MK 2 3.8 (Long term restoration), 2.5 P.I. Triumph saloon, 564 Hymer motorhome.

  2. #2
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    Did you do this :

    Following reconnection of the battery, the engine should be allowed to idle until it has reached normal operating temperature as the stored idle and drive values contained within the ECM have been lost. Allow the vehicle to idle for a further three minutes. Drive the vehicle at constant speeds of approximately 48 km/h (30 mph), 64 km/h (40 mph), 80 km/h (50 mph), 96 km/h (60 mph) and 112 km/h (70 mph) for three minutes each. This may cause a driveability concern if the procedure is not carried out. This will allow the ECM to relearn idle values.
    X-Type 06 2.0L Diesel Estate - "Schrodinger"- Now rescued from the clutches of the evil physicist.. the cat is alive!

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    Hello X-Files,

    battery reconnected and started to it's normal 1100 rpm idle, soon dropping to 750. ran for a minute or so, blipped the throttle a couple of times and back to 500 rpm idle with no reaction to the throttle. Obviously the car is undriveable but there are no fault codes to assist with fault finding?
    My next move is to check if the trhottle actuation is being reflected in the throttle position. My code reader indicates that the throttle is responding when depressed but I don't know if the reading is just the pedal or the throttle itself?

    Alec
    2004 2.5 X Type Estate, MK 2 3.8 (Long term restoration), 2.5 P.I. Triumph saloon, 564 Hymer motorhome.

  4. #4
    Senior Member Billy2Jags's Avatar
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    Check battery connections esp to earth.
    Also check alternator wiring and connections - this type of fault is usually a voltage issue.
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    Hmm.. What depth of code reader do you have? If the APP sensor (accelerator pedal position) did not create a reaction at the TPS (throttle position) then I would expect an "implausible" code.

    The P0128 ECT code is also wiring related.

    The throttle body, accelerator pedal position sensor and the Engine Coolant Temp (ECT) sensor share a common ECU signal "ground" they all ( Black/Green wires) connect at ENS6 This would appear to be between ECU and JB1-17 which is the "42-WAY / BLACK / ENGINE MANAGEMENT HARNESS TO JUNCTION BOX HARNESS ENGINE COMPARTMENT / LH SIDE"

    This same B/G sensor ground wire is on the oil temp sensor, so it might be worth doing some continuity checking as that would seem a likely suspect
    X-Type 06 2.0L Diesel Estate - "Schrodinger"- Now rescued from the clutches of the evil physicist.. the cat is alive!

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    Hello X-Files\Billy,

    slight lag due to Cristmas.

    From cold it will start and react to the throttle, presumably because the ECU is not controlling?

    The battery is giving signs of failing, and the one installed is too small anyway so that has been replced with the correct type.
    A loose earth tag on the rh front turret by the power steering reservoir found, cleaned and tightened.
    Using the code reader (Autel Auto Diag Elite) I can watch live data and the throttle is responding, confirmed by watching the throttle while my wife operated the pedal.
    Air flow sensor does not respond while the throttle is modulated possibly indicating an air flow sensor problem, but what is the reaction time? Subsequent wiring checks following the Jaguar manual instruction discovered no fault in the wiring or power supply. A negative on two tests gives the remedy of 'Replace MAF sensor', a quick check of the sensor showed the, what I think is a thermistor, was very dirty on the downstream side which I cleaned with carburetor cleaner. This made no difference.

    Is it possible for the MAF sensor to fail but not give any codes, that is what concerns me? What sort of symptoms does the MAF sensor have on the engine running?

    Alec
    2004 2.5 X Type Estate, MK 2 3.8 (Long term restoration), 2.5 P.I. Triumph saloon, 564 Hymer motorhome.

  7. #7
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    Hello all,

    my next step was to do a cold start and monitor MAF figures with the throttle being modulated. However, instead of the usual 1100 rpm and responding to the throttle it started and idled at 500 rpm with no throttle response. I disconnected the battery and left it overnight, hoping that the normal start routine would happen. But all that now happens is it won't start at all. Still no fault codes from the ECM?
    My next step is to clean the plugs, in case they have been fouled by all this poor running, but I'm not convinced that is the problem but it will help to eliminate one possible source of the non start.
    I'm beginning to wonder if the ECM is the cause of the problem now, but I've no real experience of ECMs and symptoms of failure, but the lack of any fault codes seems very peculiar?

    Alec
    2004 2.5 X Type Estate, MK 2 3.8 (Long term restoration), 2.5 P.I. Triumph saloon, 564 Hymer motorhome.

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    It is quite possible for a MAF sensor to fail or work partially without causing an error code. As the ECU relies on it to set the fuelling amount ( and therefore control idle ) this could well be the problem. I would replace the MAF sensor and then read the signals from it and see if the ECU is picking up anything from it as it definitely should be changing with more throttle applied
    2004 X Type 2.0d SE

  9. #9
    Senior Member payno's Avatar
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    Unplugging the MAF should see if run on pre set parameters
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  10. #10
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    Unplugging the MAF should illuminate a MIL light.
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