Xantia 2.0 16v Idle problems
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  1. #1
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    Default Xantia 2.0 16v Idle problems

    Hi all,

    Our Xantia has never been "nice" with its idle speed control. Previously I have asked aussiefrogs opinion about the slow returning idle & difficult speed control while driving. This turned up comments about the idle speed control servo being unreliable. I have replaced this with no effect. I have done a battery off reset to no effect. I have changed to 98 octane petrol & done another battery off reset to no effect.
    Now we have the idle being randomly high plus sharp missfiring while accellerating.

    Any pointers on where to start looking for problems?

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    Thanks all.

    FarmPug

  2. #2
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    Going back to before you changed things at the throttle area, did the car stall at slow corners or when coming to a stop? Fairly normal otherwise?

    If so, look at the motion sensor at the speedo drive on the transmission..

  3. #3
    1000+ Posts Ken W's Avatar
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    Is it missing? I have had to replace coil pack twice on mine.

    When did you last look at the spark plugs and check their gap? If they are not re-gapped, the gap can open up towards 2mm at which time the coil pack doesn't have enough voltage to fire the plug when under load.

    Put your old idle stepper back on to see if idle returns to how it was before if you prefer that.

    Do you have access to diagbox to see if there are engine ECU errors? If the engine warning light stays on for 5 seconds after you start the engine, there are stored codes in the engine ECU. Is this in a Series 1 or Series 2 Xantia?

    Have you done anything with the Crank Angle Sensor?

    and we havn't even started to talk about the manifold vacuum sensor, knock sensor or the oxygen sensor.

    More ideas to come.

    Cheers, Ken
    Last edited by Ken W; 13th December 2018 at 01:56 PM. Reason: more sensors

  4. #4
    Too many posts! JohnW's Avatar
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    Goodness. Ours just worked. For years....
    JohnW

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  5. #5
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    Another variable to confuse matters: the quality and performance of idle speed control motors can vary widely. Replaced the one on my 16v with a cheap Ebay-sourced item - it worked better than the failing original, but not very well overall and not long before I got sick of it. Similar symptoms to what you describe (except the missing under accel.)

    Solution for mine was to stump for a real deal OEM quality unit. Beautiful and reliable idling ever since

    Best of luck !
    Last edited by Harvey; 14th December 2018 at 11:50 AM.
    Harvey.

    Currently: Xantia SX wagon, C4 Exclusive, CX2200 Pallas, Xantia Activa, BMW K75C.
    Previously: Xantia Activa (the other one), Daihatsu Sirion, Xantia Activa (the other other one), Suzuki Alto, Xantia SX wagon (the other one), CX GTi, Xantia VSX CT Turbo, Honda CB250T, CX2400 Pallas.

  6. #6
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    Quote Originally Posted by seasink View Post
    Going back to before you changed things at the throttle area, did the car stall at slow corners or when coming to a stop? Fairly normal otherwise?

    If so, look at the motion sensor at the speedo drive on the transmission..
    No, never stalled. just slow to return to idle & hard to hold a constant speed on the road.

  7. #7
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    Quote Originally Posted by Ken W View Post
    Is it missing? I have had to replace coil pack twice on mine.

    When did you last look at the spark plugs and check their gap? If they are not re-gapped, the gap can open up towards 2mm at which time the coil pack doesn't have enough voltage to fire the plug when under load.

    Put your old idle stepper back on to see if idle returns to how it was before if you prefer that.

    Do you have access to diagbox to see if there are engine ECU errors? If the engine warning light stays on for 5 seconds after you start the engine, there are stored codes in the engine ECU. Is this in a Series 1 or Series 2 Xantia?

    Have you done anything with the Crank Angle Sensor?

    and we havn't even started to talk about the manifold vacuum sensor, knock sensor or the oxygen sensor.

    More ideas to come.

    Cheers, Ken
    Spark plugs are fairly new & do have a smaller gap than the worn ones that came out. The engine light does stay on for a few seconds after start up so I will need to look at error codes. Also when it misses, the engine light flashes very briefly.
    I could not get my copy of diagbox to work so I will try to find an alternative.

    I have opened and cleaned every wiring plug that I can find (crank angle sensor, O2 sensor, Gbox speed sensor, MAP sensor, Knock sensor, temp sensor, air t sensor, & possibly others)

    Are the crank angle sensors prone to failure?

    I can try the old idle stepper motor (because replacing this did not really change the problem I was chasing) but changing this was not related to the start of the missfire.

    Thanks for all the ideas people!

  8. #8
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    A leak somewhere could be letting air in. The stepper motor controls idle air but can't control a leak. Check all rubber.

  9. #9
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    Quote Originally Posted by seasink View Post
    A leak somewhere could be letting air in. The stepper motor controls idle air but can't control a leak. Check all rubber.
    I second that, it sounds to me there's an air leak. If you heave an OBD scanner, check the short term fuel trims and see whether the ECU is trying to add more fuel.

    Check all hoses in the air intake system as well as PCV valves.

    Cheers

  10. #10
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    Quote Originally Posted by seasink View Post
    A leak somewhere could be letting air in. The stepper motor controls idle air but can't control a leak. Check all rubber.
    Already done. but failed to mention

  11. #11
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    The missing plus light would fit with a coil pack on the way out. May not be the only problem.

    Kim

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    Im going back to my mi16 days but may be relivent /there was a temp sender near the t stat housing that ,let the ecu know when the engine was cold, so idle speed and richer mixture applied ,if this sender is open circuit or intermittent ,its going to mess with the idle speed and mixture ,when the engine is hot ,on the mi it was a totally different sender to the one that ran the gauge .pugs

  13. #13
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    Update:

    OK I have two separate problems, unstable idle & missfire.

    Thinking back the missfire may have started when I replaced the worn spark plugs for new (Denso Iridium). So I have refitted the old plugs and the missfire has vanished plus no more check engine light when the miss happens. This is amusing as the old plugs are quite worn with gap about 1.2mm.
    Why would new plugs gapped at .9mm with nice new sharp edges cause a random miss?
    Why would this then light up the check engine light? - what feedback is there from the coils to the ECU that would light up the check engine light when the missfire occurs? or has this come from the O2 sensor that must get a shock of unburnt fuel from the failure to ignite....

    FarmPug
    Last edited by Farmpug; 28th December 2018 at 01:15 PM.

  14. #14
    1000+ Posts Ken W's Avatar
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    I'm glad to hear you have sorted out the missfire issue. I use Bosch plugs in our Xantias.

    Although these MP5.2 ECUs are the last of the 8051 based units, they do some pretty tricky stuff. I remember reading a story that a NZ automotive training organisation put on their website about a Xantia with one of these ECUs that wouldn't run well. Apparently the crank signal is good enough for the ECU to count each individual tooth on the flywheel and it doesn't like it if some teeth are missing. Someone had done a rough clutch job on this car or bits of metal started to circulate in the bell housing because one of the teeth was missing. Apparently is was running all back to normal with a replacement flywheel.

    I think with the idle problem, keep trying different idle steppers until you find a good one. I am sure this ECU will calibrate the stepper on power up from a battery disconnection and works it hard during use. I reckon it opens up the idle circuit fully on overrun to limit engine braking and I have seen mine initially come down from higher speeds to idle at 1200 rpm and then slowly settle down to 900 rpm.

    Cheers, Ken

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