First thing to do is determine whether the problem really is related to the number one cylinder and only the number one cylinder. If you remove the number one plug wire, does the idle change at all? If it does NOT change, then the problem is definitely associated with the number one cylinder (injector? valve?).

If the engine idle gets noticeably worse when you pull the number one plug, put the wire back and try the others one at a time. That'll pinpoint the cylinder that isn't firing.

If ALL of the cylinders cause the engine to worsen when you pull their plug wires, then the problem is NOT associated with a particular cylinder. Then it would make sense to check the coil (easy to check, anyway), the timing belt, the O2 sensors, etc.