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Dan, Technician
Category: Toyota
Satisfied Customers: 24465
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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2002 toyota corolla: vacuum leak..the engine runs smooth..likely cause

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I have a 2002 Toyota Carolla with a P0300 code. Can't find any evidence of a vacuum leak and the engine runs smooth. What is the likely cause?

As you can see this is often a hard thing to diagnose. The first thing I would do is get some approved cleaner from your local parts store then clean the mass airflow sensor and replace the spark plugs and also get some injector cleaner. If thiat does not help you will need to bring the vehicle to a shop that has a smoke machine so they can force smoke into the system and visually inspect for leaks. Let me know if you have questions, thanks.


P0300 Multiple Cylinder Misfire Detected

Possible CausesSetting Conditions
  • Base engine mechanical fault that affects multiple cylinders
  • Check for air leaks in the Air Induction system (e.g., in the intake manifold)
  • Check for air leaks in the EGR system and in the related hoses and/or valve
  • Check for air leaks in the PCV system and in the related hoses and/or valve
  • Fuel delivery component fault that affects multiple cylinders (e.g., a contaminated, dirty or sticking fuel injector)
  • Ignition system problem (coil or plug) that affects multiple cylinders

Dan and 3 other Toyota Specialists are ready to help you
Customer: replied 7 years ago.
Thanks, XXXXX XXXXX me a good start. I'll get these things done on Saturday and see how it goes.
Sounds good, let me know. Thanks