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"hunting" revs? Sometimes engine revs up and down a couple hundred rpm.

Discussion in 'A3/S3 Forum (8L Chassis)' started by grue, Mar 19, 2013.

  1. grue
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    grue New Member

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    [Mar 19, 2013]
    AKL 1.6, just bought it last week (103,000km) and I'm ironing out the issues with it one by one. This one has me a bit confused.

    It won't always do it, but sometimes I'll be idling and notice the revs are oscillating between 900ish and 1100ish, or thereabouts. Never acts like it'll stall, just acts like I'm blipping the throttle every half second or so.

    Timing belt is very due for a change, but I can't imagine it's related to that?

    I did just replace the coolant temp sensor, which revealed the thermostat is boned as well, could it be tied into that somehow? Otherwise, MAF, vacuum, throttle body, spark?


    EDIT:

    Some googling around makes it sound like I'd be very well served to take off my throttle body and give it some love with carb cleaner, I'll do that this weekend. Maybe tomorrow after work if I can get a gasket. That having been said, still open to suggestions on what else to check.
    Last edited: Mar 19, 2013
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  3. Buzzer
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    [Mar 19, 2013]
    As you mentioned, throttle body or you might have a leak in the pipe work.
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  4. TwinCamMan
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    TwinCamMan Member

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    [Mar 19, 2013]
    I had a car that used to do that too, but only when my coolant level was low. Fixed the coolant leak and it never happened again. So I reckon you could be right on the coolant temperature sensor / thermostat area.
    #3
  5. grue
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    grue New Member

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    [Mar 20, 2013]
    What's the best way to test for the latter situation? Throttle body gasket "should" arrive tomorrow so I can do it tomorrow evening, might as well be ready to take the next step in testing after that.


    Also I'm kinda feeling foolish, but didn't realise until I refuelled last night that my car is supposed to use premium fuel, not the cheap stuff like my 8v Bora used. Presumably this is part of why my fuel economy was so bad on the first tank, hopefully fixing this issue gets it further up because I only averaged about 20mpg :(
    #4
  6. Danno57
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    Danno57 Member

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    [Mar 20, 2013]
    Had the exact same issue a while back, replaced the throttle body, replaced thermostat and checked pipes for leaks, the problem still persisted so I asked a garage and they said the throttle body needs re-adapting (alignment) with vagcom, so I purchased it and done the process on the Ross tech site; my car never hunted again!

    Forgot to mention: I've got the same engine code also.
    Last edited: Mar 20, 2013
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  7. grue
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    grue New Member

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    [Mar 20, 2013]
    Oh awesome. I'm gonna be cleaning the throttle body tonight just for good measure, btu I'll take it to someone with a vagcom to have 'em do that :)
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  8. grue
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    grue New Member

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    [Mar 21, 2013]
    Welp, throttle body is cleaned, but I found a bit of oil in the intake hose. When I was trying to get a better look, this happened:



    image (4).jpg


    Gaffer taped it back in place as a "wishful" attempt to patch it, and the problem is worse than before (less time between revs)


    It stands to reason that this was leaking and causing the issue in the first place, no? Then when I was in there dicking around, I broke it off completely and now it's worse?

    Still going in for the throttle body alignment in an hour or so, but not holding my breath now.
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  9. Danno57
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    Danno57 Member

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    [Mar 21, 2013]
    I guess the only way to be sure would be to have the garage do a smoke leak detection test or replace that with a new one. Let us know if the throttle alignment fixes it though, fingers crossed.
    #8
  10. TwinCamMan
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    TwinCamMan Member

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    [Mar 21, 2013]
    Looks like you'll have to go for the replacement anyway, personally would replace it before realigning it.
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  11. grue
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    grue New Member

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    [Mar 21, 2013]
    alignment didn't do much to speak of, picking up a replacement pipe later today, hopefully.
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