Mazda miata running rough.ive.took to ahop they cant figure it out either

I have a 90 mazda miata and it runs really rough like low idle around 250 rpms sometimes I can.accelerate all way to floor and nothin happens it will still idle and I have to let it warm up for a lil while before I can raise the rpms to move it but when I go to move I have to raise the rpms to 4000 or it will try to shut off ive checked mass air flow meter and ive checked timing belt also check catalytic converter and idk what else I need help no to see ody I took to can fure it out and ive ch ecked ecu to see if it was ground out anything its not plz help