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Hi, Hope you can help. I have a NB. while in idle, if I keep the car running a while, the second fan kicks in and the annoying shakes begin throughout the car, this may happen for 30secs to a minute before going back to normal, this also seems to happen randomly while driving also, any thoughts. the belt seems ok and the fan does not seem loose? asked the mechanic to have a look during a service, but it came back the same? cheers.

The fan is not belt dríven on any MX-5.
I assume the fan is kicking in, causing the revs to drop and that's what is causing the shakes?
If so, it's an electrical issue.

Second fan should kick in when air conditioning is on.
You could try resetting idle as per:
http://www.miata.net/garage/KnowYourCar/S7_Idle.html
Or as per:
viewtopic.php?f=76&t=60434

If it gets worse, sounds like camshaft position sensor might be on the way out:
viewtopic.php?f=18&t=21853

Thanks for the feedback.

The second fan kicks in while idling without the aircon on, and it doesn't seem to lower the revs all that much...then the fan will switch itself off and on again while driving, seems weird as there isn't any added load on the system? perhaps something is on it's way out? So car goes fine, second fan kicks in and I can make a milkshake with the annoying rattle.

Second fan is for air con only.
Are you sure it's not the first fan?

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I wonder if it's the sign of a dying battery?

Apart from the issue the car is having, sounds like your fans have been rewired as first fan should only come on as required, & second fan is for AC & should only come on when AC is on & is required.

People sometimes wire them in parralel but they should come on and off together if that's the case.

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Just checked and noticed that the second fan (larger) is out of alignment, causing the noise, can the plastic blades be re-aligned (popped back in) or does it need to be replaced? and can I get one from repco or SCA

The fan is held in by a single, toothed, bolt in the centre so perhaps the nut just needs to be tightened.

As others suggested, I seriously doubt the amount of shaking is caused by the fan being misaligned because if it's that bad then the shroud will start to come loose, it'll make an enormous din, etc.

thanks again, I will disconnect the fan tomorrow and see if the rattle is indeed sorted, if so, will replace fan altogether.

I wouldn't recommend disconnecting your primary fan, disconnecting the AC one (drivers side) should be fine, however.
If you can make a milkshake because of how bad the shaking is, I'd be looking at something else other than the fan.

Its wiring/ecu related.

Or IAC value not opening enough when extra load is increase by the aircon system.

If the a/c is kicking in i.e. 2nd fan then check the bearing