Try swapping injectors. Replace #1 with #3. If ## starts to show miss fire, then you know it is a bad injector. Also look for a vacuum leak around the #1 intake manifold.
SOURCE: Misfire on cylinder 1 and 3
Do you observe abnormal idle speed? It may be just an indicator fault; not a really engine firing problem.
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SOURCE: 99 4runner 5vz-fe 3.4 misfire
I know this post is old, but right on the engine theres a sticker that says use multi-ground plugs only. I read a similar problem like yours and it seemed to turn out that the spark was arcing to ground over the ceramic on the plug. So maybe it could have something to do with the single ground plugs.
SOURCE: engine code p0307 cylinder #7 misfire
It could be carbon deposits on valve seats keeping valves from totally closing. You can try getting you a can of motorcraft PM3 top end engine cleaner and get engine up to operating temp then remove one of the small vacuum lines from the intake and draw the contents of the can slowly into the engine.After you have drawn in the contents shut engine off and let it soak for about 45 minutes then crank it back up and let it run until it clears. Now it will smoke like a forrest fire while you are doing this so don't be alarmed,just tell the neighbors you are spraying for mosqitos.This may cure the problem. If not you may be looking at a valve job.
This can be verified with a compression test if this is what is causing it.
SOURCE: misfire in cylinder 1 2001 mercury sable
Next change swap the injector with another and see of the problem moves. If it does it's a bad injector.
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thank you, already swapped the injectors and replaced. Vacuum leak is our next step, could it be the intake gasket? Only missing on #1
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