I cant even tell you how many times I've seen this on many different cars, especially Honda's with distributors.

A lot of times when someone does a 'tune up' on a Honda and they replace the Distributor cap, they dont actually let the cap seat properly to the distributor base where that very small/thin gasket is and when they tighten the cap down it never sealed properly so over time more and more moisture gets in there and never gets out.

Also some people over-tighten the cap til the point that it cracks.

This actually happened on my d16y8 swapped Civic 2 days ago. The cap that was on there came with the motor when I swapped it in 3 weeks ago, it LOOKED like it was in good shape and I havent had a problem until 2 days ago when my buddy and I decided to clean and detail the engine. Water got into the cap and the rotor spins it around on all 4 contact points and than you got yourself a missfire.

She started up perfectly fine and idled fine, until you stepped on the gas and tried to accelerate...it was band enough for me to stall the car when i let off the clutch and when I finally got going the CEL would flash. A flashing CEL indicates a serious missfire...i pulled over, shut the car off and pulled the cap off...sure enough it was full of water and white carbon buildup on all the ignition points where the spark was trying to burn the water. Scrapped it all off and wiped the cap clean with a napkin and put it back together and she was good to go.

 

Doesn't matter if the tune-up has been done recently or not. If the wires were routed improperly, or if they were a cheap set they could internally leak.

Also, if it's ONLY while it's warm it could be a sensor that is out of parameter. Wouldn't be a bad idea to bar graph the ECT to see if it's functioning properly, measure resistance in the secondary ignition system, etc.