Before you throwing lots of money at expensive parts you probably don't need (what many newbies do) - do these two things:
1. Make SURE your vacuum system is tight. The easiest way to do this is replace all vacuum hoses with new ones. On the ZXs, there are two small lines that go through the firewall and are supposed to run flapper doors for the heater/AC. Those are hard to replace so for the moment, just cap them off.
2. Disconnect, clean (if possible) and reconnect EVERY electrical fitting under the hood and at the ECU. This includes injector plugs, battery terminals, fuses, fusible links, and especially ground wires. If you can get at the plugs to clean them, just plug-unplug numerous times to clean up the connections.
3. (I know I only said two things, but...) Make absolutely sure your battery is tip-top, preferably almost new.
4. Use only NGK or Nippondenso spark plugs. Don't ask me why, but nothing else works half as well.
These cars are very sensitive to good vacuum and good electrical connections. I'm guessing that ust doing these few things will make the car run much better. If it's still kinda funky, they start looking at things like gummy injectors or other fuel probs. With gas blends these days, a car that has sat for awhile, especially outside, can start to get varnishy gas. That might require flushing lines, new fuel filter and possibly getting injectors ultrasonically cleaned.