2001 3.4 V6

Hi all, I am new to the forum and this is my very first post.
I am working on an 01 Tacoma, it originally had leaking valve covers. I removed upper/lower intake plenums and associated hardware. After gaskets were installed, the motor fired right up and ran very well.

1. It started to run rough, got out my scanner and PO304, misfire #4 cylinder.

2. I cleaned the MAF, removed and sprayed electronic cleaner in each Fuel injector connection, and all removed connections.

3. I cleaned the grounds
4. I replaced vaccum hoses.

The motor still runs rough, I took everything back apart, to get at driver side fuel injectors, all cleaned and correctly installed.

Rechecked all electrical connections and vacuum hoses, no problems found.

Put everything back together and now the motor is running rougher.

I will go out and swap the coils and see if the P304 changes position. At least I will know if the coil is bad or not.

Not sure what to do next, the motor was running good other than the leaking valve covers. Because of that I have eliminated the fuel filter. I checked the EFI fuses, no defects noted.

I am not sure what to do next, any feedback will be appreciated, thanks.

~John
Up-date, I changed plug wires and PO304, has gone away, now I have PO306, with a flashing CEL, that comes and goes. I will now swap coil positions and see if the fault will follow the coil to a different position. I cleaned the MAF, again, checked all the driver side plugs and they look pretty good. Please help if anyone has a suggestion on where to go next.

Thanks

2nd Up-Date Swapped coil position, and fault code PO306 stayed in same position. I then swapped spark plug from #4 to # 6, fault stayed at PO306, both spark plugs looked very good. They both were light brown and not lean at all. Because of this, I think #6 fuel injector is good because the plug from that cylinder looked very good. Please help if anyone has a suggestion.
I feel the fuel filter is not at fault, because there are no random misfires.

 

Ever get this figured out?

 

From what I've seen recently, head gasket. I am having the same exact problem