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Thread: 2000 miata runs intermittently bad

  1. #1
    dave
    Guest dave's Avatar

    Default 2000 miata runs intermittently bad

    I have a intermittent problem with my 2000 miata, intermittently runs
    bad misses terribly then clears up just as fast. I have had the Mazda
    dealer tune it up, plugs, wires fuel filter but it still does it. It
    has a P0420 cat efficiency code in it when this happens. I have never
    been able to get it on a scanner quick enough to figure out what the
    o2s were reading and if it is missing on certain cylinders when this
    happens. My local dealer said it could be O2's, Cat, or MAF sensor. Im
    no Miata expert but I thought a rule of thumb was if the cat was bad
    the thing would be real sluggish and get worse as it gets hotter. Any
    Ideas? I don't mind putting a Cat of MAF on it just would like to try
    to narrow it down before I start hanging parts.

  2. #2
    Christopher Muto
    Guest Christopher Muto's Avatar

    Default 2000 miata runs intermittently bad

    dave wrote:
    > I have a intermittent problem with my 2000 miata, intermittently runs
    > bad misses terribly then clears up just as fast. I have had the Mazda
    > dealer tune it up, plugs, wires fuel filter but it still does it. It
    > has a P0420 cat efficiency code in it when this happens. I have never
    > been able to get it on a scanner quick enough to figure out what the
    > o2s were reading and if it is missing on certain cylinders when this
    > happens. My local dealer said it could be O2's, Cat, or MAF sensor. Im
    > no Miata expert but I thought a rule of thumb was if the cat was bad
    > the thing would be real sluggish and get worse as it gets hotter. Any
    > Ideas? I don't mind putting a Cat of MAF on it just would like to try
    > to narrow it down before I start hanging parts.


    After having the coil pack on my 95 replaced I had similar symptoms of
    intermittent rough idle, so rough that I had to give it gas to keep it
    from stalling, even when driving... the trusted mechanic I use was
    perplexed by this and confirmed that it wasn't a ground problem (a
    common problem) and knowing the cars history and solid maintenance he
    could only suggest doing a fuel injector purge (plus a new set of cables
    and plugs), and it worked. The car had about 125k on it at the time.
    Not sure if this solution would apply to you but thought it couldn't
    hurt to mention it. Let us know how it works out.

  3. #3
    Chuck
    Guest Chuck's Avatar

    Default 2000 miata runs intermittently bad

    On 5/17/2010 1:08 PM, Christopher Muto wrote:
    > dave wrote:
    >> I have a intermittent problem with my 2000 miata, intermittently runs
    >> bad misses terribly then clears up just as fast. I have had the Mazda
    >> dealer tune it up, plugs, wires fuel filter but it still does it. It
    >> has a P0420 cat efficiency code in it when this happens. I have never
    >> been able to get it on a scanner quick enough to figure out what the
    >> o2s were reading and if it is missing on certain cylinders when this
    >> happens. My local dealer said it could be O2's, Cat, or MAF sensor. Im
    >> no Miata expert but I thought a rule of thumb was if the cat was bad
    >> the thing would be real sluggish and get worse as it gets hotter. Any
    >> Ideas? I don't mind putting a Cat of MAF on it just would like to try
    >> to narrow it down before I start hanging parts.

    >
    > After having the coil pack on my 95 replaced I had similar symptoms of
    > intermittent rough idle, so rough that I had to give it gas to keep it
    > from stalling, even when driving... the trusted mechanic I use was
    > perplexed by this and confirmed that it wasn't a ground problem (a
    > common problem) and knowing the cars history and solid maintenance he
    > could only suggest doing a fuel injector purge (plus a new set of cables
    > and plugs), and it worked. The car had about 125k on it at the time. Not
    > sure if this solution would apply to you but thought it couldn't hurt to
    > mention it. Let us know how it works out.


    The NAs behave a bit differently than the NBs. The "no return" fuel
    system is one difference, as is the coil pack on the 99-01 s.
    Cam sensor failure has been a bit more common. Due to the no return fuel
    system, a pressure relief valve inside the tank on some 99s was prone to
    sticking partially open, causing starting problems.

    I ended up replacing the OEM fuel pump, not because of any obvious
    problem, but because my 99 is turbo'd and had some "raggedness" at high
    power levels. This later went away when I installed a new OEM coil pack.

    What was so frustrating was that the problems were very intermittent.
    One thing that was misleading was that use of Techron or other strong
    fuel supplements seemed to help.

    The intermittent no start, rough start, backfire, and then start
    normally on the next attempt really had me going for a long time.

    Finally, I broke down and bought a fancy timing light that actually
    worked with the miata's ignition system. This showed what looked like
    random rather than timed firing, or no firing when I was able to catch
    things in the act. Again, when I changed the Cam sensor, the problems
    seemed to go away. In the middle of all of this, I was making 500 mile
    interstate trips with little or no indications that anything was wrong.

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