I have a 2004 4Runner Sport Edition V6 4.0L with a misfire on P0306. I replaced and the spark plugs and switched ignition coil with a different cylinder and still says cylinder 6 is misfiring. Has a rough idle for about 30 seconds after starting then goes away. Not sure what to do next.

I have the same thing going on. My mechanic told me he's doing these things first:

1. PCV Valve
2. Air Filter
3. Mass Air Flow Sensor. (this is most expensive of the three but solves a Lot of these issues)

The Mass Air Flow Sensor is available from Toyota, but not always somewhere like an auto parts store. However, it comes with a 30 day return if it doesn't solve your issue.

If that doesn't work, we'll try the Injector in the 6th Cylinder.

For me, Toyota dealer jumped immediately to the head gasket. My mechanic doesn't think that is it (no overheating, no fluid leaks, etc.).

FYI, mine s a 2004 V6 4Runner with 137,000 miles

I dont have any overheating or leaks either. Seems to be common as I see it in alot of forums but no answers. Keep me updated.

I'm about to throw in the towel.... Did you find out for sure what your issue was?? Is it fixed?

I have the same problem with my 2004 did anybody find out what it was?

i had the same things happening to my truck. sadly mine was a warped block at cylinder 4. hope its not the same for you. good luck

wow a MAF sensor is a pretty rare cause for a toyota to exibit a misfire..
honestly sounds like your mechanic is hangin parts in the dark.. you can do really simple tests to see if it is working properly..

and just shake the pcv valve if it was stuck you would have really high oil pressure and be leaking oil out of any weaker seal on the motor..

did your #6 plug have deposits, oil, fuel or was it clean.. since you already swapped out coils

since you already swaped coils and the misfire didnt change then rule that out
since your dont have a multiple misfire code as well then it is happenning at pretty seperated times..

check the connector to the coil for corrosion and make sure no wires have rubbed threw..

i would definently do a compression test and cylinder leak down test with the cylinder wet and dry..

First clear codes , put in injector cleaner run that for at least one tank of gas see if codes return if codes return replace injector #6 and or bite the bullet and replace all injectors . Very comon problem in my shop.

2006 Sport with 85K. So far I have had a toyota dealer replace the #2 coil, P0302 misfire. Then two weeks later, same issue, CEL, and they wanted to do the #2 injector. They got a P0302 again with the new coil, then a P0300. Hoped injector would fix it, I said fine since they paid for the coil. Two weeks later...guess what... Same Issue. Noticed that my coolant was low. one week later, poured in atleast a quart to get to the same coolant level with a warm motor.

Suggested that the dealership check the head gasket this time. "Never heard of the head gasket going out at 85k and we see 100's of em".

Q: should I also ask for a compression test?

Just got back from the dealer. They ended up replacing a the number 4 spark plug. Told me they could not duplicate the problem once the new plug was in there. They told me they did a compression test, and everything was fine.

Forgive me I am not very mechanically inclined: This means that it couldnt be a head gasket, right?

What should I do???

i have 2004 4runner and i was having the same issues that you are. i took all the sparks out and did compression test.... not good.. blown head gasket.. water pump was bad and it was really sneaky... engine light on every once in awhile, non-stop rough idle when start then finally i had those test done and thats what it turned out to be.. 2200 later..

Just got my truck back from my local dealer after they replaced the head gaskets on both sides. To be clear, my motor was not overheating, it ran normal temp at all times. It was eating coolant, but not much. As tracyscram pointed out, the car is not going to declare its issue, you have to be a detective to figure it out. Reading over all these posts, I notice the exact same symptoms I had.

If you are baffled, and about to do something like a MAF, do yourself a favor and test for hydrocarbons in your coolant.

If it turns out that you have bad head gaskets, call toyota like I did. Stay calm, stay diplomatic, and they may just help you out. Toyota paid for all of my parts, and my rental car despite the fact that my 06 Sport v6 has 85k on it. Parts were 350, plus one week of a rental car adds up. I would have rather had them pay for all of it, but something is better than nothing.

Happy to report that its running great, and hopefully will continue to for longer than 85k more miles.

I have the same issues my 2005 4Runner, it has 161k miles on it and I've fixed the oil leak in the spark plug seal, plus I swapped out injectors on Cyl # 6 and 1. I got the P0306 error code again last night. I've done several other repairs on it all ready this year and I getting worn out! I've had my 4Runner for almost 9 years now, I'm thinking it's time for an upgrade.

Just change the head gasket and she'll be good for another 160k.

im a tech at a toyota dealer and i had a similar problem with an 06 4runner with the 6v. replace plugs then swaped coils and injector and was still getting a misfire on cylinder 6 after it had sat for a while. ended up talking to a toyota product engineer on the issue and he said he has seen a significant increase in this problem over the last year and they have determined it is a leaking head gasket that occurs around cylinder 6. so i replaced the headgaskets and the problem was solved. toyota did not offer any assistance on the bill however.