According to the book, specified standard idle speed is 1300 +/- 50 r/min (rpm) for a 2002 ZX6R. And I dare to assume that it is the same from 98-02.[^]
Your idle speed may be too low. According to the service spec, the proper idle speed is 1,050 ± 50 rpm for 49-state and Canadian models. But you likely have a California model, which should idle at 1,250 ± 50 rpm.
This info may vary slightly from that in the service manual.
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