P0304 DTC Code - Cylinder #4 Misfire

I have been getting this as a "pending" code lately. I found the good advice here that I should try to swap the ignition coils b/w #4 cylinder (all the way at the driver side) with the one next to it and see if the misfire moves to the #3 cylinder. I will do that tonight and also check the plugs condition.

My question is however, why is there no "freeze frame" data associated with this code? I cleared it once but it reappeared soon after, and I think it did it at start-up when the engine first got going, not while driving...

Anyway, I'd appreciate any other suggestions in diagnosid/fixing this problem. I will report back how it goes with the coil swap. Btw, my plugs are only about 6K miles/4 months old and are OEM Toyota part - I put them in myself and have not had this issue come-up until recently only.

 

Well, the pending code cleared itself. So I'm postponing further diagnostics until the time it reappears, if it ever does...

 

Well, if the code does not re-appear the swap won't help, so I'd rather not do it before I need to - I'm lazy

I've only seen it twice in "pending" mode (no MIL was on) so far and that was recently. If it does show-up a third time though, then it will likely appear a 4th time later, so then I will do the swap and be ready for it.

 

The code appeared again. So I swapped it, but I think I found the problem. The #4 coil bolt was loose and the coil moved about - no tools necessary to remove . That would have probably been enough to cause poor spark now & then and trigger the code. Hopefully, this was it. I'll have to recheck soon and if anything is loose, to put some thread locking compound.

 

Good suggestion. I did this and all looks clean and dry. The one bolt was loose only a little but if the engine was washed or something like that water may have entered. But nothing like this seems to have happened - there were a few rains but nothing that would put enough water in that area to go over the rised edge around the spark plug/ignition coil hole in the engine cover...

The spring inside the coil housing that makes contact with the spark plug and the spark plug end were also clean and dry, so things should be good, I hope.

The plugs themselves were tight and I did not bother to remove them this time.