I’ve had the miata “rough idle” on me a few times recently. It only does it on cold start, and it sounds like it’s down a cylinder for a few seconds, but then it smooths out again. I figured I’d check and replace the plugs again since I know #4 has been looking pretty bad. I last replaced the plugs about 5months ago.
Per usual, #4 looks fouled. The plugs measured at 0.034” gap all around; pretty much exactly what they were when installed.
I put in a new set of BKR7Es @ 0.034” gap (what they are out of the box). After the new plugs were installed, I started the car, and I think it still rough idled for about 1s. Maybe it’s just the cold weather we’ve been getting here in Florida (see 3rd photo).
Here are the photos.
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