Possible reasons for check engine light to come on?

[sammm]

Your intake/EGR port is probably gunked up. See this -

http://www.miata.net/garage/manifold/index.html

It's easy to DIY. Get a couple can of intake/throttle body cleaner and go to town. I used some weed-eater line to make sure the little EGR port was actually cleared out. You'll understand after you see the link above.

[tailchaser]

I'm sure it was nothing more than a rock stuck the tread of the new tires...

Or a loose nut behind the holding on the wheel.

[cArAzzIE]

Your intake/EGR port is probably gunked up. See this -

http://www.miata.net/garage/manifold/index.html

It's easy to DIY. Get a couple can of intake/throttle body cleaner and go to town. I used some weed-eater line to make sure the little EGR port was actually cleared out. You'll understand after you see the link above.

As it turns out - it was definitely gunked up...I hope I'm not posting too soon but so far so good! Thanks for posting that link, it turned out to be a big help. The light went out (after disconnecting the battery) and hasn't come back on yet.

Many many thanks!