intermitent engine management problem

[Matty]

which model/year do you have?

[Bevan]

No no no no. Always go for the cheapest and most simple options first.

It could just be something as simple as the plug that goes into the air flow metre. Take the plug off, spray WD40 or RP7 or equivelent into the plug and also the connection on the air flow metre. Clean contacts with a scouring pad and plug back in. See how that goes.

You could have water somewhere in the ignition system. Have you degreased the engine bay recently? When I degreased my last MX5, I was having these problems. Turns out I didn't seal the spark plug pods well enough and water got in there. Remove your spark plug leads and shine a torch down there, if there is water, throw a rag over a coat-hanger and get busy soaking up all the water. Don't remove your spark plugs! If there is no water, it wouldn't hurt changing spark plugs and leads.

Your coils maybe on the way out. A multimetre should be able to tell you this.

And 420 pound for an air flow metre?!?!?! Is it gold plated? Take it to a different mechanic, they're ripping you off badly. A brand new one from MX5 Parts in the UK is 299 pound inc. VAT. Click on the link.

You'd be able to source a good second hand one for much cheaper again. These cars have been around for 17 years, parts aren't too hard to come by.

Let us know how you get on.
Cheers,
Bevan

[sabretooth]

I'm thinking the AFM or coolant temperature sensor.

See if you can borrow bits before you go out buying replacements though.

[CT]

Idle control circuit for mine. What work has been done on the car recently?