I brought the car to Auto Zone when my check engine light came on. The codes were PO 300, 301 and 303 ( misfires). I changed the spark plugs (Iridium) and got new coils. The check engine light is still on. What can cause this to be on still?
Disconnect the 12V battery for a few minutes to clear the DTC. If the same DTC come back, perhaps the fuel injectors for cylinders 1 and 3 are at fault.
Not too easy. You have to remove the fuel rail that the injectors plug into. You have to replace the injectors without damaging the rubber O-rings that seal the injectors to the fuel rail and the intake manifold. Consult techinfo.toyota.com for repair manual info if you are serious about taking this on. You also should check fuel line pressure to make sure it is at least 43 psi when the engine is at idle speed. If lower then the fuel tank (which contains the fuel pump within) should be replaced.
Sorry so late to the party. Just finishing up my battle with the 300, 301 miss fire codes. This forum was helpful, thank you all. I missed the basics of diagnosing, replaced a 20k mile set of plugs that looked fine. Then I replaced all the coil packs. I should have switched the one with the misfire code with a good cylinder, took it for another test drive and then checked to see if a different cylinder showed the code. I can change a coil pack in less then 10 minutes now. That would narrow done if further work was needed and it was, the next step was to swap the injectors next to each other with a cold engine. That got my cylinder misfire code to move finally. I replaced all the injectors because one was leaking with the engine not running. When I pulled the injector rail without releasing system pressure there was no indication of the 44-50 # of pressure there should have been. Final test drive and after a minute of rough idle and a code rest the computer is finally clear, next week I will go for emission test.
You need to log sufficient miles so that the engine ECU will be ready for the emissions test - perhaps 100 miles or more under a variety of driving conditions, city as well as freeway. If too few miles have been driven after the DTC were reset, the ECU will report that to the emission test system and you will be asked to return after more miles have been accumulated. The purpose of that is to make sure that an owner does not clear DTC immediately prior to testing.
