Welcome to Just Answer.
You did not mention what has been looked into yet, so I will begin with some basics.
First of all the spark plug
. If it has been a while since the plugs were changed, it may be a good time to do so.
Same with ignition wires, distributor cap and rotor.
It will not be a coil issue as it is isolated to one cylinder.
Next would be a possible fuel injector issue. These models had some issues with sticking injectors.
Get some good fuel injector cleaner and try it.
If it does not free up, you may need to get them hooked up to a pro machine.
If the fuel injector is OK and the spark is good, the next step is to check the compression to verify the valves and piston rings are OK
Your questions/comments are welcome to me in a reply.