My 2002 Berlina Black/Black decided to start throwing engine light codes all at the same time. The codes are as follows gotten from my OBDII:
1 of 4 – R0301 - cylinder #1-misfires detected.
2 of 4 – R0303 - cylinder #3-misfires detected.
3 of 4 – R0300 - random/multiple cylinder misfires detected.
4 of 4 – P1399 (pd) undefined code. (I don't know what this one is)
Now, what I have done to date: Lucas fuel injector cleaner on the last 5 high-test fill-ups, with 104 Octane Boost additive. I installed a set of new high grade spark plugs (recommended to me in last S2KI post). Can anyone give me some ideas as to more places to check to eliminate the codes from the engine light that comes on every week or two showing 3 or 4 codes at a time? I’m not 100% sure but I think the codes come up during the S2K's warming up time. Example: in December's big snow the car sat in driveway to warm up and after 3 to 4 minutes got in and saw engine light was on. Drove 4 miles to work and hooked up the OBDII and got the codes as above. Since then to warm up the car without getting the engine light coming on I sit in the car with foot on accelerator maintaining 1.5K to 2.0K RPMs and everything was OK.

 

There is a sensor under the car attached to the lunch box looking thing next to the diff, I was getting codes from that (it got really wet and was corroded)

I cleaned it and fixed the problem.

I got a bunch of misfire codes and rough running engine on my CRV a few years back, was a tank of bad gas, went away after 2 tanks and injector cleaner.

 

How many miles are on the car? Swap the coils 1-2 and 3-4. If they codes come up as misfire on cyl. 2 and 4, replace those two coils.