Wondering if my misfire is just the intake gaskets

[Alexjordan22]

2000 Explorer 4.0 OHV 167,000 miles. Engine has always been dead reliable and taken care of. (The 5R55E is a different story and has been fixed thanks to this forum). We don't tow or do anything strenuous with the vehicle, it just hauls the family around mainly.

I got a misfire a month or so back, swapped plugs and all was good. Then it came back yesterday so I figured it must be the plug wires or coil since I had already done the plugs. Ended up replacing both items but still misfired while under load. Pulled the codes and got P0171 P0174 P0304 P0306.

I pulled the cyl. 4 and 6 plugs and the #4 plug looked like hell, it looked kind of rusty and did smell of coolant, and was also visibly wet on the tip but was only like a month old. After swapping just those two plugs it runs great again, no issues.

What are the odds my issue comes down to an intake gasket as opposed to a cracked head? If the head were cracked would the misfire ever go away at all like it did? I plan to do everything from the lower intake gaskets and up, just wasn't sure how an engine with a cracked head acts.

 

[410Fortune]

Very very likely intake plenum gaskets
They dry up on these models and allow lots of unmetered air into the system
Look around the base of your plastic intake where it meets the metal fuel rail...see a bunch of dirt?
I would replace intake plenum gaskets and EGR tube gasket ASAP, its a pretty easy job.......

 

[Alexjordan22]

Yes, lots of dirt down around that area. Well cool then, cause my valve cover gaskets have a slight leak as well so it'll be a good time to go through and do them all. Thank you.

 

[Turdle]

Could also have a slight lower intake manifold gasket coolant leak, since the fouled plugs were the outside cylinders. If there were a crack it would most likely only show on one cylinder.
don't forget to get 12 new o rings for the injectors. Also, while you are in there, use a thin wire brush and shop vac to clean out the injector ports in the lower manifold.

 

[Alexjordan22]

I found a gasket kit that comes with everything including the injector O rings, throttle body gasket, IACV gasket, and all the others. I had planned to take the lower manifold off and do most everything up from there, and I'll surely clean out the injector ports as you suggest. Hopefully after this we will be good to go for a while.