Hello All,

I recently done a tune up on a 05 v6 stang due to never being done. Before I started I had no issues when starting or driving.
After installing motorcraft sparkplugs and making sure that they was gap at .54 and installing new wires when attempting to start I now get a rough idle when going in reverse and at a stop.
So far I checked and cleaned each sparkplug and even used the old wires to see if the wires was a issue and still no luck. I tried the relearn process, regapping the plugs, and still no luck.
Now when I use the code scanner I'm getting a p0301 code error cylinder 1
Right now I'm unsure to pull the plug out again to regap it or just clean it cause I notice that the gapping changes ever time I check the plug again.
Even though it idles low at the light I don't want to mess with it some more and it run worse then it do.
Any advice will be helpful cause Im fresh out of ideas troubleshooting.

 

That code shows, in addition to the spark plug and wires that you've already double/triple checked, these are the potential issues:

Coil pack.

Fuel filter.

Fuel injector.

Oxygen sensor.

Burned valve.

Catalytic converter issue.

Computer woes. Which could be a bad wire in the harness.

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As far as the gap changing, yes, if they're warm, they'll be different than cold. Always set spark plug gap at ambient 'room temperature'. Same as air in the tires, hot air and tire is different than cold, and the pressure will change as such.

I'd almost expect it to be the coil pack at this point, but... you might need to do some testing to figure it out.

Relevant video that may be of help, Eric O explains things really well, shows everything regarding. It's on a Jeep, and it's a really weird coil pack to be sure, but there it is nonetheless, the information carries to any vehicle with this kind of P030x code.

I'm sure it's just a coincidence, but timing's everything, ain't it?

Hope that helps! Good luck! And welcome to the forums!

 

No need to recheck gap on new plugs with Cylinder 1 misfire. A few thousands either way shouldn't make a big difference. Either the plug will fire or not. I'd be more inclined to recheck your work in that area. Recheck your coil and injector connections. Did you break any connector lock tabs? You could change one plug wire with another to see if the engine code changes to another cylinder. You could change the plug to another cylinder to see if the code changes. Check the porcelain on the number one plug to make sure it didn't crack when you installed it. It could cause a "short" misfire.