Under the Hood: What’s up with rough-running Accord?
Good job performing some useful checks and explaining the symptoms so well.
The diagnostic trouble codes you listed are meant to tell you there are misfire conditions in each of the Accord's cylinders plus a random misfire situation. (The engine is running so goofily, the onboard diagnostics can't figure out which cylinder is at fault.) As you mentioned, a number of things could be happening here. I'll mention the most likely.
When looking to tackle a problem like this, it's always best to make sure you're caught up with standard
BRAD BERGHOLDT
maintenance on such things as the spark plugs and filters or, in the case of a Honda, valve adjustments.
Assuming all that checks out, my next area of concern would be the fuel odor you are noticing. Honda issued a service bulletin just after your car was built, advising that in areas with cool winters, it's possible to encounter exactly your symptoms during a warm snap.
Because winter fuel is blended with higher volatility to help with cold-engine performance, the fuel can wind up vaporizing too easily when you've got suddenly warmer weather and a hot engine. Your symptom is known as a "hot soak" condition, meaning a high underhood temperature (hot engine, no airflow) is causing problems.
Honda's recommended fix for Accords like yours is installing a replacement fuel pressure regulator calibrated to higher pressure (resists fuel boiling) and a replacement powertrain control module calibrated for the change.
But before spending about $700 for those parts (at least they're easy to install), I'd check the car's residual fuel pressure. If it falls quickly, that's the problem.
Your next step, if needed, will be to egg on the symptom by idling the full-temperature engine for five minutes prior to shut-off on a warm day. Wait the typical 10-15 minutes. If the restart symptom appears, quickly shut the engine off, open the hood, and heavily mist the fuel rails and pressure regulator with cool water. These parts are under and between the six curving manifold tubes atop the engine. Try restarting the engine. It may still start hard, but we're looking for an improvement or change from what's been typical. If a change occurs, the bulletin-recommended repairs are suggested.
If not, other possible causes for hot soak problems include a flaky throttle position sensor or incorrect engine coolant temperature. (Observe for correct throttle position and engine coolant temperature using the cheapo scan tool, comparing the figures to a time when the car's operating normally). Another possibility is a stuck-open exhaust gas recirculation valve. This can be verified by observing the valve's lift sensor value when the symptom occurs, which may require a higher-end scan tool. If it's above 1.25 volts, the exhaust gas recirculation valve is stuck open.