code po304 indicates that cylinder 4 had too many misfires within a predetermined period of time
My car has 135000 miles.
My car has an automatic transmission.
Hello - the P0304 indicates, as you state, a persistent misfire on cylinder 4. This could be due to a bad plug or coil on that cylinder, or a clogged or leaky fuel injector, causing the misfire. "Reading" the color of the spark plug"on this cylinder MAY provide some clue as to a fuel issue (black/brown soot means too much fuel - leaky injector; white may mean not enough fuel - clogged injector). If you need to replace coils, make sure you replace all of them, and you get the same supplier for all 4 (Denso or Hitachi) - the ignition systems on this one are a bit touchy for matching replacement parts. Replacement spark plugs are less sensitive to this. I would recommend an engine inspection by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.
Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing