92 Miata Idle Problem

Hello all,

I’m posting here out of desperation. I need HELP! We have a '92 Miata with 102 on the clock. Lately, we’ve had an idle issue where it will almost die, shoot up to 2,000 and back down again. And then after “spirited” drive, run very rough and fail to fire on all four. Had it to dealer and they changed Mass air, idle contol valve, throttle position, plugs and wires. It has new filters and timing belt. Anyone have any ideas?