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2010 Audi A4 hunting on start and intermittent rough idle

  • 25-02-2019 12:00pm
    #1
    Registered Users, Registered Users 2 Posts: 2,016 ✭✭✭


    I have a B8 2010 Audi A4 4 cylinder Diesel, about 155,000 km on the clock. A couple of times in recent weeks it's hunted pretty erratically on start. Didn't stall or anything but after a few seconds it evens out. At the same time I've noticed that the idle has gotten a bit rough and at times it can feel that the whole car is shaking, even when the car is at running temp. And actually I've noticed that it can take the car a while to get up to temp and sometimes it drops from 90 down to 70 for no apparent reason but not sure if that's related.

    I only had it serviced by an indy VAG mechanic in early December and was running pretty well at the time. Anyone have any idea what I could start looking at here? No lights coming on on the dash or anything obvious like that.


Comments

  • Registered Users, Registered Users 2 Posts: 81,220 ✭✭✭✭biko


    There could be many reasons for hunting and rough idling but it's probably best to start with a good clean of the fuel system, throttle body, etc.
    Maybe change the fuel filter and spark plugs too unless it was done recently.


  • Registered Users, Registered Users 2 Posts: 9,593 ✭✭✭tossy


    I'd be looking at coolant temp sensor and thermostats anyway, hunting on start up can be caused by a faulty coolant temp sensor.


  • Posts: 0 [Deleted User]


    I would first look for air bubbles in the fuel system. The spark plugs and throttle body I would not worry about on a diesel.


  • Closed Accounts Posts: 416 ✭✭w211


    Yes, check the temperature sensor because if the temperature drops the computer changes the strategy for cold engine.


  • Closed Accounts Posts: 2,249 ✭✭✭magentis


    biko wrote: »
    There could be many reasons for hunting and rough idling but it's probably best to start with a good clean of the fuel system, throttle body, etc.
    Maybe change the fuel filter and spark plugs too unless it was done recently.

    Spark plugs?


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  • Closed Accounts Posts: 416 ✭✭w211


    magentis wrote: »
    Spark plugs?
    and throttle body...

    Diesel have a plugs but not the sparky ones :P
    The glow plugs

    Ps. now we get the ban, ban, ban (the mod are god)


  • Closed Accounts Posts: 2,249 ✭✭✭magentis


    w211 wrote: »
    and throttle body...

    Diesel have a plugs but not the sparky ones :P
    The glow plugs

    Ps. now we get the ban, ban, ban (the mod are god)

    I did see a glow plug spark once!

    A mate of mine was trying to start his old Berlingo and got his missus to turn on the ignition while he was holding a badly damaged lead to the top of a glow plug.Said he got a fair shock off it.I know more modern diesels only have 4 or 5 volts going to them,did older diesels have 12 volts going to them?


  • Closed Accounts Posts: 2,249 ✭✭✭magentis


    If the temp sensor is telling the ecu the temperature is much higher than it is,the glow plugs probably wouldnt heat?

    Is the glow plug light coming on when starting o.p?


  • Registered Users, Registered Users 2 Posts: 2,016 ✭✭✭adocholiday


    Thanks for replies so far. Yes the glow plug light comes on and turns off before the car starts and no noticeable delay in it either. Interesting about the car possibly having the wrong temp readings, also might account for why the temp gauge can take a relatively fair while in getting to 90 and intermittently show a cooling too.

    Might have to get my hands on a code reader.


  • Registered Users, Registered Users 2 Posts: 261 ✭✭show me the money.1


    EGR valve is my bet


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  • Registered Users, Registered Users 2 Posts: 81,220 ✭✭✭✭biko


    Ah, I missed it was a daysul :D

    Either way, clean it and see if that fixes the issue.
    Worst case, you have a cleaner engine.


  • Closed Accounts Posts: 2,249 ✭✭✭magentis


    Did the indie do anything major?

    If she hasn't got a fuel filter in a while I would start there.


  • Registered Users, Registered Users 2 Posts: 2,835 ✭✭✭9935452


    magentis wrote: »
    Did the indie do anything major?

    If she hasn't got a fuel filter in a while I would start there.

    Id agree. Especially with the cold weather a few weeks ago.
    The frosty weather finished off the fuel filter in mine and it was only 30k miles since it was done last.


  • Posts: 7,499 ✭✭✭ [Deleted User]


    Have you checked the microcontroller on the 3rd wire?


  • Registered Users, Registered Users 2 Posts: 2,016 ✭✭✭adocholiday


    The fuel filter was done in October 2017. The mechanic just gave it a basic oil service in December and it was running fine at that stage so nothing major. This is only happening in the past 2 weeks or so and very intermittently so even if I took it to a mechanic he could keep it for days and not notice anything.

    I'll have a look at the few things that were recommended here and give it a shot, can't hurt as you say to give it a clean.

    @BrownFinger: what's this about the microcontroller? Is that a known issue?


  • Registered Users, Registered Users 2 Posts: 383 ✭✭Waterson


    https://youtu.be/ZDw1fG3oOTE

    Only recently experienced this set of symptoms on an Audi A4, was the DRV at fault. This is a valve on the common rail that was leaking fuel back into the return system because it wasn't sealing correctly. Part used was a genuine Bosch one. feel free to PM me for more details OP


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