90 Miata, 95,000 mi. - I have an intermittant misfire at idle that is driving me crazy. It idles fine when cold. Then starts to shudder and misfire at times when hot and idling. Runs strong and well when RPM's are increased. The problem is inconsistant. replaced plugs, wires, fuel filter and no change. Any suggestions.

 

1990 had a distributor, correct? if so, you could try a new cap and rotor. if it is electronic, you might want to look into coil packs.

check the IAC valve and the fuel regulator also.

 

Thanks for the good suggestions. There is no distributor but I have suspected the coil so I think I need to work through each of these one by one. I will let you know what happens.

 

Did the coil replacement help?