P0306 misfire

[Yotamaster]

Bought an 05 4runner with 205k. Had a #6 misfire and left bank catalytic converter CEL so I got it for $3k. Ended up replacing the cat, figuring a clogged up cat could have caused the misfire. Swapped the #6 could with #4 and replaced all the plugs. Drove it for about 500 miles during the summer and no CEL. Previous owner said head gaskets were done at 180k miles and I have the receipts.

First cold morning start it had the P0306 cel for #6 misfire. I couldn't feel or hear a misfire and it drives great. I noticed the coolant is on the low side but I haven't really been paying attention to it. I took the engine cover off and noticed the intake manifold runner near the back cylinders were slightly wet. I'm guessing the misfire could be an issue with the intake manifold and it might need new gaskets. I'm going to take it apart and see what I can find, but has anyone had an issue like this? I'm guessing the fluid there is coolant since it doesn't appear to be coming from the fuel rail, but it is so dirty it's difficult to tell.

My plan is to start the car cold, spray carb cleaner around to try to find a vacuum leak and if I don't find anything I'll take the intake manifold off and replace the gasket. I am confused how coolant runs thru the intake manifold but I guess I'll figure it out as I take it apart.

Any input from experience would be greatly appreciated, thank you guys!

 

[Drcoffee]

Just so you know coolant does not run thru the upper intake plenum. I would get a head gasket test kit and see if the head gasket has failed again.

 

[The G-Man]

Yeah, take a look at the most recent post in my thread and watch the 3 youtube links. If you have that code on cyl 6, you most likely have HG issues. Unless it actually is the coil/plug. Move them around and see if it follows.

Coolant system issues