Rustybigj

Ok just bought a 03 civic ex with 1.7 vetch as a gas saver, replaced coils an plugs, changed all fluids, fuel treatment also, problem I'm having is cylinder 4 miss fire still coming up randomly an sometimes random miss fire codes on all cylinders, the car will idle so smooth I cant even tell it's running, getting around 36mpg, but randomly sometimes you start it an it will hardly move running so rough, turn it off an re start it it's fine any ideas on what it could be???

NDNV

What is the code you are getting?
Use only Honda OEM NGK spark plugs.
Check timing. Consider a timing belt service (timing belt, acc belt, water pump, tensioner, cam/crank seals) if new to you. Every 7 yrs or 105K miles, whichever is first.
Check for a bad head gasket - common issue on this engine.
Check for a vacuum leak.

Rustybigj

I talked to a honda tech today, he thinks the timing belt has alot of slack in it, doubtful it's a head gasket burns no coolant or oil, has ngk iridium's in it car has 230k I doubt the belts been changed

NDNV

Your engine is an interference type engine where if the timing belt breaks it will damage the valves in the cylinder head $$$. This would be my priority.