We recently bought a used Mazda 3, ~85k miles currently. Before yesterday I hadn’t noticed any issues. Out of nowhere, while giving it some gas, the engine starts stuttering and/or hesitating. Letting up on the gas to just cruise at a constant speed didn’t seem to raise any issues. At idle, stuttering/sputtering/hesitating exists. These symptoms seem to only last until the car is fully warmed up, at which point they disappear completely! This happened yesterday, and I have only driven it twice. Once was to a local parts store where they diagnose check-engine-light codes. They came back with P0301 - Cylinder 1 misfire. Among other things, listed possibilities included spark plugs so I decided to pop mine out and take a look. Opening up cylinder 1’s plug, when I took out the ignition coil (which sits directly atop each plug), the thing leaked what I’m assuming is oil as I pulled it out. Just a drop, but that doesn’t strike me as normal behavior. The bottom-most end of the coil assembly (the black plastic/rubber thing that you stick on the plug) was white & crusty. I took out another one to compare, and 1) No liquid drippings, and 2) It looked squeaky clean.
So at this point my best guess is that I need to replace that coil. But I’m no mechanic, and really have no experience in this realm of spark plugs and ignition coils, and am searching for a second opinion on whether the things I’ve mentioned all point to that faulty coil.