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Thread: Engine reving on start-up / fan running on engine switch-off (after working under the bonnet)

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  1. Question Engine reving on start-up / fan running on engine switch-off (after working under the bonnet) 
    #1
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    Hi all,

    I think I've goofed-up!

    I replaced the green temp sender about 2 weeks ago (in an attempt to see if it was the temp sender or a dodgy instrument cluster causing the the wrong coolant temp to be displayed on the gauge). It turns out I have a dodgy temp guage on the instrument cluster. The car works fine but I've noticed a little odd behavior since working under the bonnnet.

    The engine over-revs (~2.5k rpm instead of 900 rpm) for a few seconds after turnign the key (without the gas pedal being pressed) and the fan can be heard running at full speed for a few seconds after turning the engine off, even after only a minute of running the engine (which it normally dosen't do). - What the hell have I done?

    There is a black saucer shaped device with a plunger going into it (to regulate airflow into the inlet manifold I guess). I wedged the plunger in the open position to give me a little more room to work on the temp sender - is it possible I've torn a diaphram etc?

    ANY insight would be greatly appreciated.
    Toff.
    [ My Cars: 2011 Caravelle SE TDI (140) LWB | 2015 L200 Barbarian 2.4 DI-D | 2015 Mini Cooper SD ]
    [ Past Audis:
    A6 S-Line 3.0
    V6 TDI Qttr | A4 3.0 TDI Qttr S-Line | S6 4.2 Qttr | A4 2.5 V6 TDI Qttr Sport | A4 1.9 TDI Qttr S-Line | A4 SE 2.0 TFSI Quattro Avant | 2.0 TFSI Roadster ]
    [ Past VWs: Mk1 GTI Cab | Mk3 2.0 Cab |
    Mk3 VR6 | Mk4 R32 | Mk4 V6 MoFo | Mk4 Golf 1.9 TDI| Mk4 Supercharged 2.0 6-speed | VW Touran 2.0 TDI DSG ]
     
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  2. Re: Engine reving on start-up / fan running on engine switch-off (after working under the bonnet) 
    #2
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    I'm assuming you're talking about the egr/anti shudder valve, take the large rubber hose off and check the flap isn't sticking partially closed,also take the 5mm vac pipe off and plug the end and see if it runs any better,you can test the plunger diaphram by sucking on it.And is the temp sender a vag oem,I would be tempted to put the old one back in.
     
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  3. Re: Engine reving on start-up / fan running on engine switch-off (after working under the bonnet) 
    #3
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    Hi,

    It turned out that the over-revving on start-up and fan running at full speed was all down to the temp sender.

    Basically I'd fitted a unit from eBay (£8) and I'd managed to snap-off the clip in the process of fitting it. Although it seemed to be securely connected, it soon worked loose, so the ECU didn't know what temperature the coolant was at - so it must have gone into "Assume the worst" mode

    The broken connector:
    4600325_f260.jpg

    I had a lovely time replacing the connector.. such a fiddly job in such a confined space! Anyhow, thanks to this guide I managed to get it done and now the problems have stopped. Despite fashioning a paperclip tool as per ther guide, I still ended up having to use a junior hacksaw blade to gently cut the existing connector open to pry the pins out! Nightmare!

    I followed nevo's advice and purchased an OEM temp sender & fitted it along with the new connector. Unfortunately my temparature guage is still reading between 50c and 90c randomly (when the engine is undoubtedly fully upto temp) so I think I'm going to send my cluster off to these guys for a repair when I have some spare cash!!

    Toff.
    Last edited by toff; 08-08-2011 at 01:25 PM.
    [ My Cars: 2011 Caravelle SE TDI (140) LWB | 2015 L200 Barbarian 2.4 DI-D | 2015 Mini Cooper SD ]
    [ Past Audis:
    A6 S-Line 3.0
    V6 TDI Qttr | A4 3.0 TDI Qttr S-Line | S6 4.2 Qttr | A4 2.5 V6 TDI Qttr Sport | A4 1.9 TDI Qttr S-Line | A4 SE 2.0 TFSI Quattro Avant | 2.0 TFSI Roadster ]
    [ Past VWs: Mk1 GTI Cab | Mk3 2.0 Cab |
    Mk3 VR6 | Mk4 R32 | Mk4 V6 MoFo | Mk4 Golf 1.9 TDI| Mk4 Supercharged 2.0 6-speed | VW Touran 2.0 TDI DSG ]
     
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  4. Re: Engine reving on start-up / fan running on engine switch-off (after working under the bonnet) 
    #4
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    Could be thermostat stuck open
    eye for an eye means the whole world goes blind
     
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  5. Re: Engine reving on start-up / fan running on engine switch-off (after working under the bonnet) 
    #5
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    Hi,

    I still need to the run a diag to see if the temp guage reading matches the measuring block value in VagCom.. if it does... that I guess your suggestion is the answer.

    It seems like a pig of a job getting the thermostat out though.. I only have ramps, should it still be perfectly possible to do on the driveway?

    Toff.
    [ My Cars: 2011 Caravelle SE TDI (140) LWB | 2015 L200 Barbarian 2.4 DI-D | 2015 Mini Cooper SD ]
    [ Past Audis:
    A6 S-Line 3.0
    V6 TDI Qttr | A4 3.0 TDI Qttr S-Line | S6 4.2 Qttr | A4 2.5 V6 TDI Qttr Sport | A4 1.9 TDI Qttr S-Line | A4 SE 2.0 TFSI Quattro Avant | 2.0 TFSI Roadster ]
    [ Past VWs: Mk1 GTI Cab | Mk3 2.0 Cab |
    Mk3 VR6 | Mk4 R32 | Mk4 V6 MoFo | Mk4 Golf 1.9 TDI| Mk4 Supercharged 2.0 6-speed | VW Touran 2.0 TDI DSG ]
     
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  6. Re: Engine reving on start-up / fan running on engine switch-off (after working under the bonnet) 
    #6
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    Is your engines stat at the back of the alternator?if so its a piece of cake.
     
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  7. Re: Engine reving on start-up / fan running on engine switch-off (after working under the bonnet) 
    #7
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    Hi,

    I changed my thermostat this weekend and.. Wohooo, temp guage now quickly gets upto 90c. My car has now done 166k so I think the original thermostat did quite well!

    It was a pig of a job in the usual ways.. coolant drain plug wouldn't come out, thermostat housing wouldn't de-couple from the hose connection and I dropped one of the thermostat housing bolts which took me forever to find

    The joys of working on an old/ high millage car! At least I know she should warm-up quickly in the winter months now!

    Toff.
    [ My Cars: 2011 Caravelle SE TDI (140) LWB | 2015 L200 Barbarian 2.4 DI-D | 2015 Mini Cooper SD ]
    [ Past Audis:
    A6 S-Line 3.0
    V6 TDI Qttr | A4 3.0 TDI Qttr S-Line | S6 4.2 Qttr | A4 2.5 V6 TDI Qttr Sport | A4 1.9 TDI Qttr S-Line | A4 SE 2.0 TFSI Quattro Avant | 2.0 TFSI Roadster ]
    [ Past VWs: Mk1 GTI Cab | Mk3 2.0 Cab |
    Mk3 VR6 | Mk4 R32 | Mk4 V6 MoFo | Mk4 Golf 1.9 TDI| Mk4 Supercharged 2.0 6-speed | VW Touran 2.0 TDI DSG ]
     
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