Having Misfire codes P0300,P0302, P0303

[jgravlin]

This issue started on a trip in the mountains misfires from a complete stop at low rpm, but above 2300 rpms the engine is strong and no misfires. I have codes P0300, P0302, P0303. Had to drive it home 2 hours it would only misfire below 2300 rpm more so around 2000 rpm intermittently. When I got home I checked cylinder 2, and 3 spark plugs they look normal which I figured they would. I then moved coil 2 to position 6 and coil 3 to position 1 and drove vehicle misfires started after the 4runner is warmed up and still misfires from idle to about 2300 rpms intermittently (I changed all plugs and coil packs about 4000 miles ago). Now I only have P0300 not sure where to go from here because the engine runs so strong perfect above 2300 rpms. If I try WOT from a stop engine misfires intermittently until about the 2300 rpm mark then runs great. This is a 4.0L.

 

[MikeinNH67]

Are you losing any coolant?

 

[Warwicke36]

I'd start with a compression test. If that's good check fuel trims.

As mentioned above, check coolant level... Could be hwad gaskets (may show in compression test)... I just did my head gaskets on my 04... But cylinder 4 and 6 are more common. FWIW i had 0 misfires.

 

[importman]

This issue started on a trip in the mountains misfires from a complete stop at low rpm, but above 2300 rpms the engine is strong and no misfires. I have codes P0300, P0302, P0303. Had to drive it home 2 hours it would only misfire below 2300 rpm more so around 2000 rpm intermittently. When I got home I checked cylinder 2, and 3 spark plugs they look normal which I figured they would. I then moved coil 2 to position 6 and coil 3 to position 1 and drove vehicle misfires started after the 4runner is warmed up and still misfires from idle to about 2300 rpms intermittently (I changed all plugs and coil packs about 4000 miles ago). Now I only have P0300 not sure where to go from here because the engine runs so strong perfect above 2300 rpms. If I try WOT from a stop engine misfires intermittently until about the 2300 rpm mark then runs great. This is a 4.0L.

I had a very similar situation about a year ago. The two cylinders you named are on different banks with different coils and different injector drivers so if yours, like mine, started misfiring on both of them at the same time you probably have a similar problem to mine. It didn't make any sense, (I'm an ASE Master Tech), and so I ended up calling the Identifix Hotline. The most important thing I learned from the Toyota expert is that you can't trust the Toyota misfire monitors. I'm almost positive mine was on #2 and #3 also. So it's very likely that only one of them is misfiring, (that's how mine was). I'd suggest disabling one cylinder at a time while the engine is misfiring. To do that just unplug the connector at the coil. If it doesn't misfire at idle you may have to get someone to powerbrake it to make it misfire. Whichever cylinder doesn't affect the running of the engine when you disconnect the coil is the dead cylinder. As weird as it may be, mine turned out to be a spark plug. I replaced the plugs and it's run great ever since. If I had just replaced the plugs to start with I could've saved a lot of frustration and the cost of the call to Identifix. But I wouldn't have learned about the unreliability of Toyota's misfire monitors. The guy said you simply can't trust them. He was right in my case.

 

[jgravlin]

I drove the vehicle for a while and finally got it to throw codes for cylinder 1 and 6. As crazy as it sounds both coils went bad at the same time. I replaced them and all is good now thanks for all the suggestions.


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