misfire/idle high

Discussion in 'General Motoring' started by snuffy, Jul 22, 2004.

  1. snuffy

    snuffy Guest

    My 2002 sc1, 1.9L, sohc, always shows the same codes. Cylinder #1 misfire
    and idle higher than should be. Any ideas?
    snuffy, Jul 22, 2004
  2. snuffy

    uknewwho Guest

    Do you mean P0300?
    P0300 - Engine Misfire Detected
    I don't see any error codes referring to misfire with cly 1-4.
    Is this the only error you get? Have you had any major work done, such as
    relaced the PCM or crankshaft? If the PCM or crankshaft is replaced, the the
    crankshaft must be relearnd.
    Have you tested the spark plug wires? resistance should be between 1.5k-15k
    ohms. try replacing spark plugs and wires, if error still occurs, try
    replacing coil packs
    Try checking for vacuum leaks, often causes a high idle.

    Thats all i can think of now.
    hope that helps

    uknewwho, Jul 22, 2004
  3. snuffy

    snuffy Guest

    Thanks!..P301 and P507 possibly just the way my reader deciphers them and
    it's just a general misfire but the OBD P code chart says P301 is a
    number 1 cylinder misfire.........Changed the wires and plugs, even did
    the resistance test on the wires and all good. Looks like coils are next.
    For past few days the weather has been hot and muggy and the idle has been
    around 800 rpms. This morning it's very cool and dry and the idle was at
    1500 rpms again.
    snuffy, Jul 23, 2004
  4. snuffy

    uknewwho Guest

    800 RPM is ok, the spec is 750 +/- 50.
    Could be your IAC Valve (Idle Air Control Valve), This controls your
    throttle plate opening at idle. If you have a Haynes book it's page 4-11
    section 15.
    So if you want to start cheap, i'm sure a iac valve is cheaper then 2 coil
    Also, just a though, your plug wires are routed the same way as stock right?
    I know this will cause some strange problems if the wires arn't done right.

    Hoped that helped
    Good Luck

    uknewwho, Jul 23, 2004
  5. snuffy

    snuffy Guest

    Yep the wire routing is the same. Guess I'll try the IAC valve. Thanks!
    snuffy, Jul 23, 2004
  6. snuffy

    C. E. White Guest

    Mis-fires are detected by measuring the rate of change of
    the crankshaft speed. If the cranshaft doesn't speed up
    enough after the cylinder has supposedly fired, then the
    computer records this as a mis-fire. This means that you
    can't just look at ignition problems. A misfire can be
    caused by an the injector that isn't supplying enough fuel,
    or a leaky valve, or whatever reduces a particular cylinders
    performance relative to the other cylinders. I spent 3
    months trying to clear a mis-fire condition on my SO's van.
    We changed plugs, plug wires, distributor caps, etc. Turned
    out the problem was a burned exhaust valve on the offending
    cylinder. The vehicle always seemed to run OK, but it would
    set a mis-fire code with days of clearing the code after a
    repair (even the local Chrysler dealer kept trying to blame
    the ignition system).


    Ed White
    C. E. White, Jul 26, 2004
  7. snuffy

    snuffy Guest

    I was wondering how it detects a misfire. There are no sensors on the
    wires for sure. Probably should do a compression test and see if number 1
    cylinder is low. Oil consumption jumped all at once also. Though it shows
    no oil fouling on any plugs. Very good info! Thanks much!
    snuffy, Jul 26, 2004
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