Hi
Back again with my 1998 Honda Civic misfire. It now has 133,700 miles on it.
So far we have replaced the plugs with NKG ones, new plug wires, rotor and cap, fuel filter. Then Sea Foam to gas tank thinking bad gasoline. New ignitor. Next error code came up for catalytic converter. Replaced that and O2 sensor.

It behaved for about 5 weeks, then I started noticing an intermittent low idle which almost stalled the car. Then it started missing at highway speeds and not accelerating well. Gas mileage is really variable, from 30 mpg to 36 mpg. Today it started running really rough when I first started it and engine warning light finally came on, flashing. I drove 1 mile and pulled off, shut car off, waited a few minutes and restarted the car. Light quit flashing but stayed on. Noticed some misfire while driving 65 mph.

Only other thing going on was that we finally got rain after about 6 weeks of drought.

Engine error codes today at Auto Zone were 0300, 0301,0303,0304, and 1399

You have done a lot of good things; however, I would also replace the coil. Since you are throwing misfire codes on multiple cylinders, the coil could be the culprit. I recommend replacing coils at 120,000 miles or 10 years, whichever comes first. If the problem persists, after replacing the coil, there may be a problem with the distributor; e.g. a bad Crankshaft Position Sensor. The distributor housing would then need to be replaced.

Thanks for good advice txgreasemonkey. We did replace the ignition coil. Still had a problem after that, just misfire cylinder 1 this time. So we replaced the sparkplug wires again and distributor cap and rotor and sparkplug 1 with Honda parts. It seemed to idle better and run great for about 150 miles. After driving 60 miles, it ran rough in town while driving 30 mph. Next day ran great with me driving turnpike speeds. Next morning driving home, it started running rough while I was going 65 to 70 mph on the turnpike. No error codes have shown up yet, just sporadic rough running which goes away after a few minutes or less.

Hi I understand you wrote this in 2008 but I was wondering if you ever found out what was wrong with your car because my honda civic 97 dx did the same thing but has been broke down for 4 months and seems like no one knows what's wrong... my car was misfiring and then it seemed like I was going slower on expressway then the meter read... then one day I got into my car and my lights inside were dead my boyfriend put a bigger fuse in the fuse for the lights and it poppped... then a week after thaat my car just shut off. If you have an suggestions or answers to your car it would be great I'm in serious need of my car. Plzz and thanks. :)