I have been seeing this alot lately on 10 diff cars within a month all d series civic, seems most have been 02 probs, 1 Cat, coolant sensor and fuel relay on warm up, bad tps (only after they have removed and put back on without ohm meter), bad injector,plugs, wires, cap & rotor, coil, bad connections to dizzy, im just throwin this up so peeps have a place to start there troubleshoot, on all of these cars i have gotten the same codes even though problems were diff. you will get a check light with this prob and under load it will flash alot of the times.

A code P0300-P0304 may mean that one or more of the following has happened: Cyl Missfire

* Faulty spark plugs or wires
* Faulty coil (pack)
* Faulty oxygen sensor(s)
* Faulty fuel injector(s)
* Burned exhaust valve
* Faulty catalytic converter(s)
* Stuck/blocked EGR valve / passages
* Faulty camshaft position sensor
* Defective computer

nice little write-up