HELP!!! My 1993 Nissan Sentra has 200,000 miles on it runs great replaced all the tune-up parts and the catalytic converter and it just barly fails emission test H/C's too high at 25mph can anubody out there help me?
Hydrocarbons are unburned fuel, so I would replace the O2 sensor and air filter if you haven't already, double check the ignition timing, and try cleaning the MAF sensor (ONLY use MAF-SPECIFIC cleaner for this!).
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