Miata prob

Just found this forum and need help with a car i just bought. Starts right up and idle is smooth (about 8-900 rpm). If I slowly increase speed to 1200-1300, it acts like it's going to die and of course it hesitates (bucks) if you try to drive it off in first gear. If I let it idle at the 800 level for about 2-3 minutes, everything is completely normal. As a wild guess, I'm thinking it's related to transition from open to closed loop. Checked for codes...none. I could really use some help on this. If necessary, email me at mdpar (at) beecreek.net. TIA

Put in new wires and plugs. Miatas will chew through both. Let us know if that helps.

O2 sensor sounds likely. Also coolant temperature sensor.

I second the wires and plugs. New NGKs for both and it took away the low rpm stumble on mine.

Mine exhibited similar symptoms but my problem got worse after the engine warmed up. Turned out to be the coolant temp sensor, so from what you are describing I think you can scratch that off the list.