2000 1.8 stumbling

Hello MX-5’ers,

  1. My model of MX-5 is: 2000 Icon 1.8
  2. I’m based near: Thame, Oxon
  3. I’m looking for technical help or recommendations on: Engine stumbling and power loss

This is a problem of an engine stumbling at idle, and running erratically when crusing at a steady 30mph.

Video: MX5 engine stumble - YouTube

It’s very low mileage, and back in March it had a service at a Honda dealership, since when no problems have been noted until just the other day. I wonder if this might be temperature related in some way, due to our current heatwave as it came on pretty suddenly when the weather got hot?

In the service the following was done (among other checks):

  • Oil and filter replaced
  • air cleaner replaced
  • plugs replaced
  • valve clearance adjusted
  • timing belt
  • transmission fluid

She also got a new camshaft sensor in oct 2020.

Grateful for any suggestions on where to begin! (Current plan is to pull the plugs tomorrow and see if they show any useful pointers).


Check for oil on the plugs when removing. Honda dealership may not have used a genuine Mazda cam cover gasket whilst changing the belt, inferior ones can cause leakage which in turn leads to oily plugs or leads.

Coil packs can give trouble too on the Mk2, worth changing out the plug leads as a process of elimination too.

Just looking back through parts receipts, I see an ignition coil, lead set, and spark plugs in Apr-2000. Seems odd that the plugs were also replaced in 2021 so maybe they looked in poor shape already, or it was just a “might as well do it”.

I see two listings, for DAY4PK855 and DAY4PK885 poly rib belts, but nothing for a cam cover gasket, so … they didn’t replace it? Definitely sounds like a good shout though, so I’ll check the plugs tomorrow.

Thanks for the help.


Is it a misfire?
If so, will be electronic/spark related.
If it is ebbing and flowing rather than misfire stuttering, more likely to be fuel related…in my opinion.
Both fuel systems and Electronic systems can have heat related issue.
Regardless, I would run a diagnostic check for error codes using the jumper and LED method on the diagnostic port as a start. Do not disconnect battery or ecu as codes will be lost.
Possible good call on next post which ironically is an electronic issue affecting fueling; should produce an error code. This is a MK2 model though, so no OBD diagnostics, just old skool LED interrogation.

might be worth ODBII reader check - I had similar symptoms on my 2001 1.8 and it was the MAF sensor

@rhino666 I’m not sure about whether it’s a misfire or not - feels much like it though. It seems significant that it’s intermittent, as I’m wondering whether an electric problem would be more consistent?

Would you expect to a CEL if the diagnostics had found an issue?

@longrider thanks for the tip. It sound like I might be out of luck on the OBDII by a year or so though?

Well, update on Day 2.

Pulled the plugs - they looked fine to me but I’m No Expert. Threads had oil on them … it that normal? The electrodes seemd OK (probably about 1,000 miles on them, no more than that), but let me know if I’m wrong on that.

(can only upload one image, but they’re all pretty much the same).

This morning she started fine, idled well, came up to temperature, and was driven home about 20/25 miles without any hint of a problem.

I’ll have a look at the LED diagnostic test next.


The plug threads should be dry, I can see the oil especially on the sealing ring. Unless it’s left over from the cam cover being removed (doubt it) it seems you may have a leaky gasket.
Shine a light down the plug holes in the cam cover, any evidence of oil down there?

Will do! I’ll see if I can get a photo. Thanks Mick

Update on this: clean as a whistle under the cover, and our local garage had a look at it but couldn’t find anything wrong.

However, it’s still not running right. It’s a hot day (29deg here) … could that be a factor? We’ll wait until the weekend when it’s cooler I think, and see how it’s running then.

Could be that we really need someone who knows these cars better, so any suggestions for someone in the Thame, Oxon area would be appreciated.

That plug gap looks rather large…

Sorry for the late reply.

Yeah, worth checking I think. I would have thought that that would cause rough idling all the time though, and that doesn’t seem to be the case here. The plugs are pretty new also.

Quick update again: after running very rough on a hot day, it was completely smooth on a 3 mile drive over the weekend when it was only 20C. After sitting for about 5 minutes, it was back to rough running on the way home.

Is there something heat related that can go wrong with these?

Don’t forget on “cold” from start up eg ECU enrichment…or sensor controlled leccy choke if you like… can serve to confuse the issue. Note…after around three miles the ECU should not be making it run rich. In my experience with both ours…usually a mile/ mile & half at most unless sub zero.

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Not sure if your model has one of these as I was experiencing similar issues running Rich ect after few miles so I replaced this


Looks promising! I’ll have a root around, but it would be a neat little fix. Thanks for the tip!

Hi slimdave any luck with the car after I fitted the above sensor mine runs lovely

Hi Dave any luck