After a 2 hour journey, I went to start the car again, and the check engine light came on. It would come on, then flash, then stay steady. Car was running roughly at times.

Had an OBD scan and that error code came up. Curious if anyone has had similar instances. I'm wondering if it's the ignition coil, or the spark plug. Car is 9 years old (never had plugs changed) and has 34,000 miles on it (yes, a crime I know).

thx.

 

That's a cylinder 3 misfire code. Nine year old plugs could very well be the issue. You might swap the #3 with one of the other plugs and see if the code jumps to the other cylinder. P0301 is #1, P0302 is #2, P0303 is #3, P0304 is #4.

 

If it does turn out to be just the spark plug, at 9 years, would it make sense to just to a whole tune up? Or just replace the bad plug and call it a day?

 

If your code, after swapping #3 with say #4, jumps to #4, you'll know it's the plug. It could also be the plug wire in which case your problem would stay in cylinder 3. I would never replace just one plug, particularly with plugs this old. Best to replace all four. If it's your wires, best to replace all four of them as well. Good luck.

 

Had the spark plugs replaced and it still thru the code. Replaced the ignition coil and all is well.