97.5 GS. About 20,000 miles ago i did a complete tune up. Plugs, wires, air filter, pcv valve, gas filter. the plugs are Iridium. Supposed to last forever.... The wires were standard AC Delco. They look good. No cracks. Is it time to replace? How often should PCV be changed? Filter is K+N....How often should i clean it out? I also found there is a filter for the supercharger bypass valve but have never replaced it...any idea's? I also used Techron fuel injector cleaner. Does this stuff really work, and how often should it be used?