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Wierd thing i noticed last night after giving it a lil.
WHen i come to a stop the idle sometimes drops and rises from like as low as 500 rpm to about 1200. up and down as if it is searching almost.
a quick blip of the throttle fixes it, just wondering if this could be a sensor or something? would love to know

should be covered in detail here somewhere.. or on miata.net but its usally a dirty gunged up idle control screw.. time to clean out the intake manifold

thanks mate... i thought it would be something like that. just didnt know where to start.

i replaced the OXYGEN SENSOR with a Repco replacement. idle problem instantly fixed. just thought i would put this up there in case someone else tears there hair out..

Dweezle wrote:i replaced the OXYGEN SENSOR with a Repco replacement. idle problem instantly fixed. just thought i would put this up there in case someone else tears there hair out..

Did you put in a single or 4 wire?

Part number?

single wire.. not sure of the part number.. just walked in and said i need a Oxygen sensor for my 1990 mx5.

they gave it to me for about 60 bucks. cut the wire put new one in, re crimped.. all good

I've also been considering getting a new 02 sensor and the SA Repco distribution centre is literally 200m down the road from my work so i went investigated...

For all those wondering I believe the part number is ...

Bosch (single wire) universal O2 sensor : 02 5898 6501
which i got quoted $61
(so i think this may be the same one you got Dweezle)

From Bosch.com:
single wire sensors typically last up to around 50,000kms
multiwire sensors generally up to 100,000kms
Dud sensors can basically cause -
rough idling,
lack of power,
fuel wastage and also surging or hesitation and general bad engine performance.

So it sounds like a item that needs to be replaced on most NA6's having high kms.

L.

Yeh thats the one... Made a world of difference..
and was so easy to do

Thanks Dweezle & Lucky Luke
I've been trying to figure this one out for over a year. Opinions on this problem are usually quite varied.
I'm off to Repco

Let me know how it goes.. Hope it helps you as much as it did me.. i was so relived after i did it and pulled up at the first set of lights and have the car just drop to 850rpm and stay there

Purchased a single wire sensor from Repco (NGK/NTK brand made in Japan) for $21
Same model number as the Bosch, clearance sale apparently. Normal price was around $57.

my mx just started doing this but the battery light has started flashing too (that might be a loose wire somewhere) are the nb8 02 sensors the same as the na?

MXHEVN wrote:my mx just started doing this but the battery light has started flashing too (that might be a loose wire somewhere) are the nb8 02 sensors the same as the na?

No, they had a 4 wire sensor and are more expensive (early = single wire). I don't have the part number for this sensor.

Dweezle wrote:...WHen i come to a stop the idle sometimes drops and rises from like as low as 500 rpm to about 1200. up and down as if it is searching almost.

Also try your leads. It happened to my other car. Once warmed up, on idle (usually at traffic lights) the revs would drop (from its normal level), then the car's brain will rev it automatically to prevent it from stalling. It's like a see-saw. It will do this all the time, to the point that I used to keep presure on the go pedal to keep revs up, when stopped.

Took it to a mechanic and they diagnosed the problem as the leads. They replaced them and have never experienced the problem since. That was over 12 months ago.

Bad Leads usually cause the car to miss under load so if the problem is at an idle only it's unlikely to be leads