P0301 once only

I have a 2007 Mazda3. My wife drove the car two miles, and parked it for two hours. The startup was rough and the check engine light (P0301) was blinking. She restarted it with no improvement and drove two miles home. Since then, I cleared the code and the problem has not returned, after 20 or so short trips. Is any action suggested? I understand multiple items might be wrong, and intermittents can be hard to diagnose.

I would swap the coil to another cylinder, if the problem comes back and the cylinder changes you likely need a new coil.


Just remember which one you swapped it with… lol


At my age, remembering is the hard part.


Keep in mind that a flashing check-engine light means that damage is likely to occur, so I wouldn’t do this again.

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As you say, there are many possibilities for a misfire. I recently discovered the cause of my truck’s intermittent misfire, spark plug wire, conducted ok when cool, but no connection when it got really hot. I was led to the ignition system b/c it would start very easily, even though it was running poorly just before. I was led to that particular wire b/c when I wiggled the spark plug wires & boots to see if that would affect the misfire symptom, I got a little shock, but only on that wire. This suggested the extra boost the ignition system gives during cranking was overcoming the problem, confirming an ignition system problem. Suggest to try to come up with some clues like that. Does it misfire only when hot? Only when cold? Only when weather is damp? Do you see any visible sparking jumping around the engine compartment when viewed idling in the dark?

Weekend update
Since the time I first wrote, I have driven this car numerous times around town and recently on a 1000 mile weekend. All startups have been normal except for a single stuttering startup when the car had cooled for an hour. Of course, I was 500 miles from home. In this case, no check engine light appeared, and the stutter disappeared.
QUESTION: do the cans of fuel injector cleaner in a tank of gas really work?

Marvel Mystery Oil and Sea Foam are about the only 2 I would use, I’m sure there are others out there also… But don’t over due it as they can leave deposits on the valves and pistons etc…
The old saying is if some is good more is better is not true in this case… lol
Build up flaked off and got under the valve head…

You really should check both ends of the spark plug wires to see if they are firmly connected. If you don’t know how to do this either take the car to a mechanic and ask them to do it or learn how. A loose wire can do this sort of mischief.

This car has no plug wires. An ignition coil sits on each spark plug. The low voltage wires to these coils look OK.

A dose of Techron fuel injection cleaner in the gas tank probably helps. I can’t say it makes the engine run better, but seems to help w/emission testing results a little. I just follow the instructions written on the product. There’s a local fuel injection cleaner I’ve used with some success as well, but I don’t think product that is sold anywhere outside the SF Bay area.