85 Sunbird LE- Hard start-runs- Then when warm Missed

I have a 85 Sunbird LE. 1.8 OHC. when I g to start it I have to turn the key 3 times to the on position count to 4 turn it off and then on the 4th time turn it all the way to crank and it starts. It runs ok, with lots of power and no misses until it reaches about 120. 15-20 minutes later, at that time it will start to miss. As if it had a bad plug. I have replaced the spark plug, wires and the fuel pump. Any thoughts what it could be? This car has 83K and almost everything has been replaced.
Thank you

Check for codes?

Check fuel pressure?

Check coil output?

Check for vac leaks?

If it runs rough at idle, what happens if you remove the air cleaner and LIGHTLY spray carb cleaner into the throttle body?