Intermittent misfires on cold start/acceleration only

Hello,

I have a very well maintained 99 Civic LX with about 140,000 miles on it. Starting in January I began having an intermittent misfire problem. The problem only occurs while the engine is cold and only during acceleration above 3000 RPM. When it does happen, I can lift my foot off the gas pedal and it will immediately go away for a minute or so (or until the engine reaches normal operating temperature).

A little more info: the MIL comes on and I receive a code for O2 sensor, but I'm fairly certain this is an effect of the misfiring, not the cause. If I clear the code it will not return until next time the misfiring returns. Even if I don't clear the code, the problem will recur.

I have tried several different brands of gasoline and no change.

The plugs and wires were installed in July of last year. I pulled them out and double-checked the gap and torque, all seems to be in order. The cap and rotor are in good shape.

I'm beginning to suspect a possible ignition coil failure. Any thoughts?

thanks in advance!
-Mike

I'm not sure it would be an ignition problem since your results seem to be dependant on temperature (when the engine warms up.) Given that temperature affects fuel/air mixture I would still look at the O2 sensor (especially since you're throwing codes that reference it.) There should be two, one at the exhaust manifold and another post-cat. Try doing the first one (requires a side-slotted 5/8" socket or something.) Yes, they're on the expensive side, so steal one from a friend's Civic to test. I wish you successful results.