I am the original owner of a 2004 V6 4Runner. The vehicle now has just under 175,000 miles on the odometer. Up until now, the vehicle has been bullet-proof.

Early summer 2019 the engine started throwing a code, alternately P0300 and then P0302. Not wanting to replace parts in ascending order of cost to end up not getting to the problem, I brought it to a local mechanic who was, heretofore, reliable. He said it was a bad head gasket as evidenced by a fouled plug and traces of coolant in a cylinder.

This is the worst possible news, but I'm glad I didn't spend $500 replacing parts that wasn't ultimately going to correct the issue. So I think I'm pretty smart at this point.

So I take it to the dealer I bought it from because their head gasket replacement quote was actually cheaper than the mechanic.

The dealer removes the cylinder head and sees nothing wrong with it - at all. Nonetheless, they replace it anyway and put in new plugs. Bill to dealer? $4,000... and I'm still getting the P0302 code.

I then personally replaced the following:

All the coils
All the fuel injectors
The PCV valve
The mass airflow sensor

Still getting the code.

Frustrated and with a ton of money in it now, I bring it back to the dealer who replaced the head gasket and tell them of my woes. They keep my 4Runner for a week and then threw up their hands and told me they have no idea. As a seeming hail Mary, they suggest testing the fuel injectors to ensure they work... another $200 to do this check, no repair or replace, just check.

Nope. We're done here.

So I still have the 4Runner. It misfires and runs pretty rough, but is drivable. And not a sole, not even the dealer, knows what to do. I'm at my wits end.

Anyone?... anyone!

Check for vacuum leaks, use some carburetor cleaner and while the engine is running spray all around the intake where it seals to the heads and all vacuum lines, if the idle changes, you have a leak and that needs to be fixed and could possibly be the issue.

Check the connection on the cam sensor, most likely not the issue but could cause a P0300 code but usually not a specific code like your P0302 but what have you got to lose.

Check your fuel pressure as well.

It could also be the ECU, but not sure of that just a thought.

You can also try running the engine at night and look at the engine while it's running in complete darkness and see if you see any sparks/short to ground especially around the number 2 coil.

If I think of any other things you can check I post again, good luck.

Looks like I'm not alone...

I am the original owner of a 2005 V6 4Runner. The vehicle now has just under 172,000 miles on the odometer. Up until now, the vehicle has been AMAZING/bullet-proof.

Winter 2017 the engine started throwing code, check engine light on, not running smooth. A neighbor who is a Toyota mechanic replaced all the spark plugs ($$$), the problem didn't go away. I also brought it to a local mechanic, he replaced the one coil ($175), the problem didn't go away. Parked the car for over a year. Brother in law, ran the code again and replaced a fuel injector and gas cap ($$$), run smooth but didn't pass the smoke check. Another local shop ran the code and replaced one Cat Coverter and 'dealer' gas cap ($$$$). Passed smoke check but check engine light was back on again. Brought it back, another coil replaced ($$$). Run smooth but two days after check engine light was back on again. Taking it back again on Tuesday.

Frustrated and with a ton of money and TIME in it now.

"When the code P0302 is set in the Powertrain Computer, it means that the Misfire Monitor has detected more than a 2 percent variance in RPM between the firing of any two (or more) cylinders in the firing order." Copied from Google.

This sounds like a stretched timing chain that skipped a little bit out of time. But then, I thought there was a specific code for that. Hmmm

how are your fuel trims?
hope you have an obd tool, read off the LTFT & STFT.