Ok, Ill try to keep this as short and to the point as possible.

2005 Mazda 6, 4 Banger. Currently showing code P0301 which says is a Cyl 1 misfire.

Let me explain the symptoms and when this is happening and hopefully someone can give me some direction.

Misfire is essentially non-existent below 1k and above 3k RPMS. If you accelerate very slowly, just a little but of pedal, it often wont do it at all, but if you dip in to the throttle some it will buck and stumble and very clearly misfire. Sometimes it will backfire afterwards (this tells me we have fuel). If you kinda keep at it, it'll buck and stumble its way through acceleration until it gets above 3k and starts to level out, then stops and runs fairly smoothly again. Sometimes it will still act up for a second or two above 3k, but my guess is the cylinder is flooded and it takes a second to get it all burned out. If you floor it from the get-go, or floor it once it starts misfiring, it will usually stop (this might be because it just gets up above 3k RPMS so fast its less noticeable, I dont really know).

Cruising at a steady throttle usually doesnt cause the misfire, ie, if Im on the interstate and cruise it at 60 or something, even if the RPM's are below 3k it will usually run just fine. This is, I assume, because it takes so little pedal to maintain the speed and as I mentioned earlier you can sometimes avoid the misfire by barely giving it any throttle.

The problem is at its worst when the car is cold and gets better as its driven and warmed up - but its always there. Sometimes it will go away entirely, only to pop back up randomly while driving. Car idles fine, unless its cold out and the idle goes above 1k RPMS, then it stumbles and acts like a jerk.

Thoughts on possible problems? Could this be a coil issue? The plugs and wires are new-ish, replaced when we got the car, which was, call it 6k miles ago, maybe less.

Ive read issues about the cats on these cars, but if that were the case I would think the problem would get a lot worse the higher the RPM, not better like it does currently. As far as I can tell Im not mysteriously losing any oil and there are no temp issues. This problem has been going on, and getting steadily worse, for weeks now. My situation is such that I HAVE to drive the car and havent had the money to fix it until now - Its awful for it, but I had no choice. I'm hoping to dive in and start fiddling around in a few days and was hoping someone here may be able to give me some advice on possibly causes.

 

Swap the spark plug with cylinder #2
Swap the Coil with cylinder #3 ( How many coils do you have? )
Swap the HT lead with cylinder #4

See if the missfire moves to another cylinder.

Try swapping the Fuel injector to another cylinder.