OK guys heres the story:

I bought the car a 04 s2000 berlina black with 31,800 miles. Now the problem when i bought it, it had misfire codes form 301-304 and p1399. Then i cleared the codes and put in new plugs thinking that would do the trick nothing. Did a search not really what i was looking for. The code then came back on and now it only reads on cylinder 4 misfire. I asked a couple of honda gurus and they think it might be the coil. So i switched the coil from 3 to 4 and from 4 to 3. Now i waited to see if the cel would come back and it did after about 50 miles of driving, reading the same code so i guess it wasnt the coil. Now i am stuck trying to figure out what it might be. It runs fine goes into vtec but idles a little rough and has bad gas mileage does probably about 200-215 miles to the tank. So i am guessing injector but still dont know please help me out here. Thanks!

 

You can always switch injectors too to check your theory.

I'd do a compression check. #4 seems prone to problems if people run their '2k's low on oil.

I never saw more than about 20-22 MPG out of mine.

 

For my AP1:
All Highway (1 VTEC per 200 miles) 30-33mpg
Mix highway/Local (1 VTEC per 10 miles) 24-26mpg
Spirited (1 VTEC per 1 mile) 20-22mpg
Fall Colors Tour ( Almost continuous VTEC) 15-18mpg