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Does it idle rough when hot? Sounds like a timing problem or a clogged fuel filter.
Has the timing belt been replaced in recent times?

Worst scenario is that the belt could have jumped a cog which could possibly give these symptoms if you have checked everything else.

VVT system playing up?

o2 sensor dead.

To check just unplug it and see if it drives smooth again.

Dann

Upon thinking about this a bit more it certainly could be the fuel filter as the symptoms you describe are similar to my experience some years ago and I replaced the filter and it was fine. If it is faulty it will certainly affect the car under power and through the rev ranges you describe and then even out as you back off a bit.

Worthwhile replacing it anyway if it hasn't been done for a while...

Mine doesnt have o2 sensor so no pics from me.

At the back of the cam cover there is a plug with a SINGLE wire leading down to the exhaust manifold, unplug that.

It WILL trigger an engine light until its plugged back in.

Dann

NitroDann wrote:Mine doesnt have o2 sensor so no pics from me.

At the back of the cam cover there is a plug with a SINGLE wire leading down to the exhaust manifold, unplug that.

It WILL trigger an engine light until its plugged back in.

Dann

It would probably be easier (and less likely to be confused with another plug) to follow the exhaust pipes from the engine down, about where the 4 separate pipes join in to one should be a thing sticking out with a wire going to it, that's the oxygen sensor.

I had this exact same problem about a month ago, I changed the fuel filter and that sorted it out.

not entirely sure what mx5 OP has but considering he has a 6th gear would indicate its a nb so i'm fairly sure it has stepped away from the primitive 1 wire o2, would more likely be a 4 wire o2 sensor. And hks kansie is right, just follow the your exhaust tract all the way to the exhaust port and you should be able to find it.

I agree with Dann - my NA ran like crap when I drove it more after purchase - I replaced the O2 sensor (NA sensor is a standard Repco part) and turned it into normal car..

Az wrote:anything else?

Another consideration might be coolant temp sensor for ECU at the rear of the head. They were a common problem on the NA6 causing cold idle/ running issues, but much less so on the NA8 & NB8.