common causes for a p0300 code on 2001 Hyundai Sonata

car stumbles slow to get to speed and doesnt want to shift

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2 answers
Not knowing any maint. history of your car and how many zillion miles , I would agree with tdtoolbox and add that you should have it checked afterwards with a scanner with 'live data' capabilities to confirm that ALL is fixed.
random misfire do a complete tune up