idle goes up and down
Dirty or faulty idle air control valve. Clean or replace as needed
dirty or faulty idle air control valve cold idle. dirty or faulty egr valve when warm.
If it is a ZX2 it doesn't have an egr, the timing belt could have slipped a tooth or a vacuum leak can cause this. I've even seen a bad battery / alternator cause it when it was undervoltage. Put a voltmeter on it and see if it is at least 13.5 volts to rule that out at idle.
The blade on the backside of the throttle body can cause this as well as others have mentioned the IAC usually gets carboned up.
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