so I get this code(P0307) the other day and tooks the plug out to check it and being they arent that much , I threw a new set in. I checked the plug wire/s as well but could not find anything wrong. I am still getting the code. The misfire can barely be noticed at idle or driving around the city but when going up big hills or getting on the gas heavy, then you can hear it. What should i be looking at next, i know this case as nothing to do with a vacuum issue for its only one plug and not a random code.

 

It always helps if you identify what you're working on....

Probably a weak coil or, if an older system, a bad plug wire. Possibly and injector or internal mechanical issue.

 

A few months ago I installed new Motorcraft/Autolite plugs in my Navigator and it ran great for about 3 days and then started missing under load. I scanned it and got a P0301
code. I pulled the plug after checking the connections at the COP and injector and found it all okay. I then pulled the plug and it looked good, I tried checking the gap and that's when I found the plug had a bad electrode, it was completely loose in the porcelain.
I suggest that you pull the plug and check it as you may have the same problem. No charge exchange at the parts store. No more problem, just a PIA to have to do the work over and go fetch.

 

Just to avoid confusing anybody that reads this thread, you meant P0301, correct?

 

Yup... Doggone dyslexia. I try to proof read all I type but I still screw up.

 

You're not alone...I got so depressed when I learned I was illiterate, that I quit reading.

 

Well thanks to the few that replied asnd gave their thoughts/opinions. My problem ended up being a bad plug wire, bad boot section on coil side. I found this out in somewhat in an amazing way. while the engine was running I was unhooking the injector clip and rehooking it once i heard the change i was looking for, after hooking the injector back up i went to move alittle to the side and doing so, my left hand landed on the coil pack and received a shock. Looking better at the wire, i could see where i was losing the spark power.

 

Boy, things like that will help you find a spark leak, FAST!
I prefer to look under the hood with the engine running at night. If there is any spark leakage it can be entertaining as well as helpful.
Glad you found it.