engine light came on, now has a misfire, or rough idle
was running fine, then lost power and now has a rough idle at a lower RPM with a check engine light on.
Go to AutoZone or Advanced Auto Parts and have them read the code for free. There are many reasons for the light to go on.
Mark is spot on! The other solution and more fun is to learn how to diagnose yourself. Pick up an official service manual from Toyota or Haynes manual if the first is not available from the dealer, then read on. All I need to diagnose my Toyota truck is a bent paper clip stuck into the appropriate terminals. Pretty cool.
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