EJ25 Liberty RX (Legacy) hiccups at cruise

Discussion in 'Subaru Legacy' started by Clifford Heath, Jan 1, 2008.

  1. Folk,

    This has been a problem on and off for a while now. It came on
    again a couple of Km after a refill at a station we don't normally
    go to.

    The engine behaves fine under acceleration, but within a few seconds
    of cruise, will start to hiccup, losing power totally for half a
    second, and repeat that irregularly *every few seconds*. It's quite
    jerky - annoying almost to the point of being undriveable, and I'm
    also worried that it might be doing damage - pinking? If you
    alternate between slight acceleration and lifting the foot, it
    doesn't seem to happen - until you stop changing speed for ~2 secs.
    The acceleration response is fine, so I don't think it's the fuel

    I suspect that the ECU has detected cruise, and is experimenting to
    find how much it can lean out the mix... but is going too far. I
    suspect the O2 sensor. Given that this is expensive to replace, is
    it possible/easy to expect to *try* a replacement before committing
    to paying for it? Apart from just replacing it anyhow, is there any
    other option?

    Has anyone else had this symptom or can suggest an alternate cause?

    Clifford Heath.
    Clifford Heath, Jan 1, 2008
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  2. Clifford Heath

    bigjimpack Guest

    Bad gas? Finish the tank fill with gas you know is good and add a gas
    line antifreeze to remove water and see what hapens
    bigjimpack, Jan 1, 2008
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  3. Clifford Heath

    noyb Guest

    Don't think so - we've been through 5-10 tanks of gas
    from our regular sources since it started happening
    again recently. Also used injector cleaner, which does
    seem to help a bit, maybe. We only ever buy premium
    gas in any case. Dirty gas will foul the filter and
    cause problems on acceleration, but this is at cruise.

    Clifford Heath.
    noyb, Jan 1, 2008
  4. Clifford Heath

    Todd H. Guest

    o2 sensor is a frequently mentioned item that explains all sorts of
    strange driveability problems.

    My own experience, however, was that a timing belt replacement caused
    me hell like you're experiencing. Not exactly the same, though. My
    stumbles and bucks were intermittent and on accelleration (reliably at
    4k rpm when it happened--and maintaining 4k rpm as a cruise speed
    would exhibit bucking that was annoying, but not undriveable) and on
    deceleration around 1250 rpm. Turns out a bad timing belt tensioner
    led to a flattened a tooth on a new timing belt when was slipping
    periodically by one tooth, causing my woes.
    Todd H., Jan 1, 2008
  5. That's good info Todd. I'm trying to understand exactly what the
    effect was caused by. Surely if the timing belt slips the timing
    will be off permanently? Or was it just sending a spasm down the
    belt by jumping on the tensioner only?

    Clifford Heath.
    Clifford Heath, Jan 1, 2008
  6. Clifford Heath

    Todd H. Guest

    It seemed like it was slipping back and forth, and the ECU was able to
    adjust to compensate...but only to a point.

    Took nearly all of 2007 to get to the bottom of it.
    Todd H., Jan 1, 2008
  7. Clifford Heath

    Fred Boer Guest


    I had driveability issues recently caused by a bad O2 sensor. It was more
    prevelant at startup when cold than at cruising speed, but it did sometimes
    happen at cruising speed with a warm engine. Usually it happened when I
    lifed up off of the gas. It was as you describe, though, bucking and
    surging. And it was intermittent. And the Check Engine Light wasn't
    triggered as you might expect.

    Initially it was diagnosed as an ignition coil - later, correctly identified
    as a bad O2 sensor. FWIW... Good luck!
    Fred Boer, Jan 1, 2008
  8. Sounds like it might have been climbing up on top of the tension
    idler, then dropping back into the notch, and causing tension
    changes that advance both cams (or retard - is it on the trailing
    or leading side?). I guess a tight/failed idler bearing will do that.

    I need to do the cam cover gaskets anyhow, maybe the idler is easy
    to do at the same time. Tackle the O2 sensor only if that doesn't
    cure it.

    Clifford Heath.
    Clifford Heath, Jan 2, 2008
  9. Clifford Heath

    Todd H. Guest

    My situation was caused by a defective (brand new, OEM, Subaru) timing
    belt tensioner not pumping up to tension on a brand new belt after the
    engine had been hand turns the designated 3 or whatever times
    (specified in a TSB on the issue) when a new belt was isntalled. A
    tooth on the belt was flattened in this initial startup sequence and
    wasn't found until months later.
    Todd H., Jan 2, 2008
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