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Hey y'all,I have a 2007 FJ with 160,000 miles and it is randomly throwing a P0304 code at startup. I have swapped plugs, swapped coils,bench cleaned and swapped injectors. Checked wiring harness for burns or splits,Checked connections ect... What am I missing? Attached logs from diag reader
 

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Hey y'all,I have a 2007 FJ with 160,000 miles and it is randomly throwing a P0304 code at startup. I have swapped plugs, swapped coils,bench cleaned and swapped injectors. Checked wiring harness for burns or splits,Checked connections ect... What am I missing? Attached logs from diag reader
By "swapped plugs", do you mean you replaced them with new plugs, or simply swapped the plug in cylinder #4 with a plug from a different cylinder?

The correct thing to have done would have been to pull ALL the plugs and carefully compare color and especially the presence of deposits on the plug from cyl #4 .

Early 1GR-FE engines with high mileage have some history of head gasket leaks that allow a tiny amount of coolant to enter the cylinder after shutdown. The engine typically runs a little rough immediately after a cold start, and the OBD code is set at this time. It seems that the problem is more prevalent on cyl #6 .

1. Do you ever notice a few seconds of rough running immediately after a cold start?
2. If you monitor OBD continuously after a cold start, when is the code set?
3. Is there any history of slight coolant loss?
4. What is the vehicle build date?
5. Have you performed a compression test to eliminate a sticky valve as a suspect?
 

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Have pulled all plugs, they do look good with the exception of #4 which had some fowling on it but nothing major. It does seem to be a rough idle issue on cold starts. Haven't noticed any coolant loss. Did a system flush and changed thermostat at beginning of year. Door sticker says 03/2006
 

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Have pulled all plugs, they do look good with the exception of [URL=https://www.fjcruiserforums.com/forums/usertag.php?do=list&action=hash&hash=4]#4 [/URL] which had some fowling on it but nothing major. It does seem to be a rough idle issue on cold starts. Haven't noticed any coolant loss. Did a system flush and changed thermostat at beginning of year. Door sticker says 03/2006
If you have absolutely eliminated ignition coil, ignition coil wiring, and leaking injector as possible causes, then (unfortunately) a very slight coolant leak past the head gasket is looking more probable, especially given the build date.

I think Toyota modified the head gaskets later in 2006.

Here's a YT time-lapse vid showing R&R of head gaskets on a 1GR-FE in a 4Runner with a small coolant leak into cylinder #4. At 20+ hours even with shortcuts, it's not a trivial job: :


Please keep us informed ...
 
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