306 GTi6 surging idle
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  1. #1
    1000+ Posts pottsy's Avatar
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    Default 306 GTi6 surging idle

    Hi everybody. Just dipping the toe in here from over in the Citroen pond.

    Son's 306 GTI6 has developed a puzzling problem. When started, the revs want to head skywards and stabilise at around 4000 rpm, which is noisy, annoying, and definitely not desirable.

    A "blip" of the throttle will bring the revs down to a manageable level, but the idle then surges between normal and about 2000 rpm in a cycle of about 1 to 2 seconds.

    Looking at the throttle body I've identified the main components I think. Throttle position sensor underneath and MAP sensor on top to the left of the butterfly (enginewards, if that makes sense).

    There is a flat arrangement on the radiator side of the throttle body which I suspect may be the idle stepper, and another smaller sensor on the engine side of the body which I suspect is perhaps inlet air temp (IAT)?

    Disconnecting each of these in turn has the expected result, to a point. Without the connection to the TPS, revs rise up to the 4000 rpm mark again. Disconnecting the MAP sensor makes the engine die.

    But disconnecting either of the other two has no effect.

    I understand that if I disconnect the TPS with the ignition off, the ECU will set default values and still run. Is this correct? (I've yet to try that).

    Also considered doing a power off ECU reset, but at this stage I don't want to lose any fault codes stored within. My el cheapo Chinese OBD thingy won't talk to our 1999 model 306, so I suspect asking it to communicate with the 1997 model is doomed to failure.

    So what I'm asking, basically, is has anyone had similar symptoms and what was replaced or repaired to solve them?

    Apparently there's a history of problems with the TPS used in these, a Bosch 0 261 230 012 unit. This I find surprising as Bosch products are generally of reasonable quality (and by the photo I took from underneath it's a genuine unit)

    I'm also aware of history with the idle stepper motors on these (and Xantias). Some time ago the owner of this car (No 2 Son) removed the throttle body and cleaned everyting, which resulted in a large improvement to the rough running he was experiencing at the time. Not sure whether to go that far yet as I'm hoping I can pin the problem down to a specific sensor or module.

    Any thoughts peoples? (Diagram added for clarity)

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    Cheers, Pottsy
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    Last edited by pottsy; 4th April 2011 at 04:40 PM.
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  2. #2
    Fellow Frogger!
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    Unknown is idle stepper, remove, clean stepper and seat. Clean butterfly. If problems persist consult live data diag.

  3. #3
    1000+ Posts BIGRR's Avatar
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    Default Crook Idle stepper motor?

    My guess is the stepper motor.

    Disconnect the air cleaner hose from the throttle body and look for a hole (inside the body) about 10(?)mm diameter just on the outside of the butterfly.

    This hole lets air past the butterfly to the down stream side of the intake, the stepper motor controls the amount of air bypassing the butterfly and controls the idle speed.

    With the motor idling (too fast?)stick your finger over the hole and see if this brings the idle speed down.

    My 205 (306) motor did this not long ago so I pulled the stepper motor out and apart (seeing it was stuffed anyway and I pulled the connector and left it off) and placed a bit of 5/16" rubber fuel hose behind the pintel, of a length that would leave the bypass passage (hole) around the butterfly blocked off completely. Yes the car is hard to start when dead cold. It takes about 40 - 50 seconds till it idles correctly but I saved a bit of "dosh" on a new stepper motor.

    Try it!

    Good Luck
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  4. #4
    1000+ Posts pottsy's Avatar
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    The plot thickens!

    Tonight I pulled the throttle body off the car. A good cleaning with carby cleaner and it sparkles like new.

    The item I flagged on the above drawing as possibly the idle stepper is no such thing. It's a temperature sender which is pressed firmly against the throttle body housing by a spring, presumably to monitor temperature.

    If it's meant to be the inlet air temp then there must be quite a lag there.

    The item at the back of the body seems to be the inlet air temp, so I'm a bit confused as to what the other one is for.

    There is no idle stepper motor on the throttle body at all!

    Anyway, the housing with the mystery sensor in it also has two tubes going away. A large one appears to be the crankcase breather via a valve arrangement beside the inlet manifold.

    The smaller one appears to disappear down under the inlet manifold to a point as yet unknown.

    The orifices leading into the throttle body from where these tubes terminate were dirty, but not clogged. They're pristine now anyway.

    I suspect that if the car has got an idle stepper assembly, it's probably down there at the business end of the smaller tube.

    Investigations will continue. (Once I can find the 306 manual! But it probaly won't help with the GTi6 anyway!)

    The strange thing, however, is that the car now starts and idles normally, but is very sensitive to throttle movement.

    I haven't discounted a dodgy throttle position sensor yet, but it measures between 1Kohm and 2.6 Kohm between closed and wide open throttle, with a smooth and linear transition.

    As far as I can tell there are no spots where it's open circuit, but of course that may not show up while juggling a multimeter and the unit in one's hands.

    More anon once I've done some reading.

    Cheers, Pottsy
    Last edited by pottsy; 6th April 2011 at 06:28 PM.
    Buvito Ergo Sum!

    The Fleet:

    2018 C3 Shine ("Oscar" Mrs P's)
    1974 D Special Manual Sedan ("Moby Dick")
    2006 C5 HDI Wagon Auto ("Mephistopheles")
    1982 2CV6 ("Gaston") Seasoned traveller
    1975 GS Pallas ("GiSelle") Current project
    And for Fun, 1968 Mini Deluxe ("The R & D'luxe" 1078cc, Grin Factor 100!)

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  6. #6
    1000+ Posts pottsy's Avatar
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    Thanks guys.

    The link was exactly what I needed (and thanks for the PM as well).

    Now I know where it is, we should be able to solve the issue once and for all.

    Certainly all the symptoms are pointing towards this being dirty. I had a similar problem with the Xantia but at least on that the stepper is visible, accessible, and attached to the throttle body where one would logically expect it to be.

    More news as it comes to hand. With any luck Betty will spring in to smooth idling life once more, the owner will be happy and I'll get Zaphod the Xantia back!

    Cheers, Pottsy
    Buvito Ergo Sum!

    The Fleet:

    2018 C3 Shine ("Oscar" Mrs P's)
    1974 D Special Manual Sedan ("Moby Dick")
    2006 C5 HDI Wagon Auto ("Mephistopheles")
    1982 2CV6 ("Gaston") Seasoned traveller
    1975 GS Pallas ("GiSelle") Current project
    And for Fun, 1968 Mini Deluxe ("The R & D'luxe" 1078cc, Grin Factor 100!)

  7. #7
    Sans Pond. STALLED's Avatar
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    The stepper motor should be under the intake manifold - it's not hard to get to!
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  8. #8
    1000+ Posts pottsy's Avatar
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    Once again Aussifrogs has come up trumps.

    Thanks to the excellent links to the gti6 forum as well as guidance from here, Betty is again terrorising the streets of Melbourne and the owner has recovered his usual broad grin.

    It seems that it was indeed a dirty seating of the idle stepper valve, as removal, cleaning and replacement has restored Betty's smooth idle.

    Thanks again, Pottsy
    Buvito Ergo Sum!

    The Fleet:

    2018 C3 Shine ("Oscar" Mrs P's)
    1974 D Special Manual Sedan ("Moby Dick")
    2006 C5 HDI Wagon Auto ("Mephistopheles")
    1982 2CV6 ("Gaston") Seasoned traveller
    1975 GS Pallas ("GiSelle") Current project
    And for Fun, 1968 Mini Deluxe ("The R & D'luxe" 1078cc, Grin Factor 100!)

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