I've got an '07 manual 2.5i that I've had for about 5 years now with 52k on it. I'm a full time student so I don't use it at all really while I'm at school. About a month ago when it was pretty cold for a couple weeks (never got above 20F) she started up with a CEL and an obvious misfire. I let it sit since I was so busy with school work and had no reason to drive it until after I could look at it.
A few days ago I started it up and drove it around and everything felt and sounded fine. I changed the air filter since the old one was pretty disgusting, I feel bad for letting it get that way since it's one of the easier maintenance tasks to perform. I also dumped a bottle of fuel injector cleaner in it and then filled it up with gas but I haven't even driven it 50 miles since then.
The CEL is still on so I had a classmate I know who has a computer scanner paired with his iPhone help me out and it read a P0303 (cylinder 3 misfire) which seemed odd to me since neither of us felt it sounded or felt like it was misfiring any longer. I tried to clear the code but I don't really know if his device had the capability to do that. I also went to Autozone and they gave me a real simple one to use (only one they had with only 3 buttons on it) and it read the same error code. No luck clearing the code. We have an auto shop on campus where we can rent tools and use of their scanner on an hourly rate so I decided I should just change the spark plugs. Well none of the three auto parts stores in the areas carry the NGKs, they would all have to special order them. The issue I have is that my spring break starts at the end of this week so I wouldn't be around when the plugs came in anyway.
My question is, if the car is reading a misfire code (which may or may not clear) but feels fine, drives fine, acceleration feels good, and no stuttering or backfiring, will I do damage to it by driving it the 180 mile 3 hour trip home before changing the plugs? I don't want to burn out the catalytic converter but I'm not feeling/seeing any symptoms other than the CEL that would tell me I might.
Thanks in advance for any thoughts guys. Regardless, I'm going to change all 4 plugs as soon as I can, just hoping I can get home to do it.