98 ZX2 trbl.code Missfire cyl.#1, Help

My 98 ZX2 started bringing in the Ck engine lite a few months ago it seemed to miss a little when the code came in. had the codes pulled at Auto Zone. (Missfire cyl.#1). Replaced plugs, wires, fuel filter and ran some fuel treatment in it. Run good for 3 weeks with no codes. Now the code is back, and the car runs very poorly most all the time. Now and then you can feel where its tring o fire on all cyl. Last I checked there is only the one code.
Anyone have any ideas what to try next.
Thanks
Mike

Possibly a worn/loose timing belt?

Pull the plug on #1 cylinder and inspect it for damage. Do this if the code for misfire is on this cylinder. Valve seat could have dropped on that cylinder and fouled the plug up. Maybe the boot isn't fully on the plug. Vacuum leak near no. 1 cylinder is a possibility. Also, a plugged fuel injector could be the problem. A misfire is almost always the wire, plug or coil pack.