I just purchased a nice MX5 with only 34K and in great condition. The check engine light started to come on after I refueled with Regular Unleaded. I have reset the light by disconecting the battery negative terminal, but it comes back on after a couple days driving. The ECV seemed OK and their are NO other symptoms. I will seek dealer guidance, but is their anyone that has had similar experience? I just refueled with Premium and will see what happens.

 

For any realistic diagnosis, you need to get the code from the ECU. Somebody in your county has a code reader; find that person or go to Autozone and have them read it. Get that number and c'mon back.

I'd do it for you, but it's quite a hike!

 

Where are you located? MI as in Michigan? In that case you have a 1.8L and we need to know the code for it.

I would NOT go to the dealer unless you like to give your money away.

 

Or better yet, buy a code reader off of amazon for like $20.

 

lots of hype for the ScanGauge OBDII reader/tool.

Lots of choices out there:
http://www.miataturbo.net/showthread.php?t=60538

I use the UltraGuage, it's just Ok

 

OK, so I re-fuel with premium gas and I am into the second day with out a return of the check engine light. I guess I have answered my own question. Thanks for your replies.

 

She only needs 87 octane. Maybe do a Seafoam to get rid of the carbon from someone not driving her the way she intended before you bought it and no more need for premium after that.

Use the revlimiter and rev that for a bit! She will thank you.

 

BTW, the scanguage/ultragauge are handy for more than codes. You can see your REAL temps, not what the BS dumby gauges are telling you as well calculate Fuel Consumption/RPM/etc.

I highly recommend the investment. There are even cooler ones out with Bluetooth that use Android/iOS and support Datalogging.

 

I an not sure what you mean by "driving her the way she intended". Thanks for the tip on the ScanGauge OBDII and Seafoam.

 

I have total confidence in your CEL lighting for you again. Get the code, and let's fix your car!