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Thread: MK1 Mazda MX5 import suspected electrical problem causing no start/rough running

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    MK1 Mazda MX5 import suspected electrical problem causing no start/rough running

    Don't know if anyone is able to help but my mother in law has an import 93 mx5 that's giving me a headache.

    Basically it is very reluctant to start but when it does fire (after the 6 or 7 attempt) it runs relatively well. However if the air con is turned on, every now and then the revs will become erratic, dropping and rising on there own. From what I can tell, the rough idling starts with the click of a relay (passenger side). This brings the air con fan on and I think the compressor,I would understand a small change in revs but this is +/- 500rpm. Then it settles for a bit but then, presumably, the relay drops out and the fan and comp go off, revs fluctuate, finally settling. This continuously repeats.

    Other things worth noting are that the rev counter works at nothing other than idle (anything engine speed other than 800ish rpm and the tacho drops to zero). Also the coolant fan is permanently on with the ignition but off again when engine is running.

    Does anyone have any ideas or experienced anything like this before? Let me know if you require anymore info

    Thanks, Craig

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    Racer Decade Plus User savvi's Avatar

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    Re: MK1 Mazda MX5 import suspected electrical problem causing no start/rough running

    Check your charge rate with a volt meter, could be alternator not charging correctly.

    It might also be just the belt slipping or the air con clutch playing up ?
    Autoelectrical & Diagnostics in Oxfordshire www.savvi.co.uk

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    Re: MK1 Mazda MX5 import suspected electrical problem causing no start/rough running

    Thanks for the quick reply

    I have just checked and the belt is pretty loose, squeeled like mad when finally got it started. I presume tightening this will calm the erratic revving when the air con kicks in and out? Or is there more to it than that? Should the air con be coming in and out, i would have thought when switched on it should stay on or is there some sort of feedback in the circuit? I will check the voltage when I have my meter. It turns over fine but just doesn't fire until it decides its ready

    Thanks again

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    World Champion Decade Plus User caprimentle's Avatar

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    Re: MK1 Mazda MX5 import suspected electrical problem causing no start/rough running

    maybe the iscv (idle speed control valve) flutering about? as the air con kicks in the iscv should control the idle, if its playing up that will cause irratic idling.
    its not dead till it's buried!


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    Re: MK1 Mazda MX5 import suspected electrical problem causing no start/rough running

    It could be the icv, it would explain the struggle to start and the fluctuating idle, is there anyway of testing it without a replacement?

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    World Champion Decade Plus User caprimentle's Avatar

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    Re: MK1 Mazda MX5 import suspected electrical problem causing no start/rough running

    i've heard you can take them off and soak them in petrol for a while to stop it sticking then bolt it back on, see if its any better.
    its not dead till it's buried!


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    Re: MK1 Mazda MX5 import suspected electrical problem causing no start/rough running

    The idle control valve has been changed and made no difference, same symptoms as before. Any other suggestions?

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    World Champion Decade Plus User caprimentle's Avatar

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    Re: MK1 Mazda MX5 import suspected electrical problem causing no start/rough running

    does it do it with the air con compresser unpluged?
    its not dead till it's buried!


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    Re: MK1 Mazda MX5 import suspected electrical problem causing no start/rough running

    Is it 1.6 or 1.8?

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    Re: MK1 Mazda MX5 import suspected electrical problem causing no start/rough running

    Quote Originally Posted by caprimentle View Post
    does it do it with the air con compresser unpluged?
    I will check and report back

    Quote Originally Posted by Bob2 View Post
    Is it 1.6 or 1.8?
    1.8

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