I have a 1998 Honda Accord EX V6 3.0L with 210,000 miles on it. At around 125,000 miles it started having the same problem that several people have asked about. It doesn't want to start after it has been sitting in the sun with temperatures being above 85 degrees. It's fine if the temps are the same but the car is in the shade its only when it's been in direct sun. My car has a bonus problem along with this though. If I start the car, drive it for a distance, then stop and turn it off for a moment (enough time to get gas, stop @ rest area, run into convenience store, etc.) when I go to start it again it starts but then I put it into gear and it stalls. At this point when I try to restart it it acts and sounds like it's been flooded. I have to sit and wait (usually when I'm half in and half out of a parking spot or just not far enough out of the space where another car can pull up behind me to get to the gas pump) for about 4 to 5 minutes and then the car starts right up as if nothing had happened. About a week ago though I had a new experience with this situation in which I was driving in town, stopped at a stop light, proceeded through the light once it turned green and got about halfway through the next block and the car just up and died. No sputtering or jolting just stopped running. Fortunately, I was able to coast off the road into a parking lot and again I set for up to 5 minutes, then it start right back up. Started like there was never a problem. I could handle all of it before but now with it just up and dying while driving down the road I've decided I need to act on this problem. Installed new battery less then 6 months ago, I've used fuel injection cleaner for the gas and have noted no difference. I do have continuous illumination of the check engine indicator and when I put my decoder on it I get a reading of P0401, which is "EGR valve, lift sensor malfunction". I replaced the EGR valve with a used valve - cleared the codes - light came back on. Thinking I maybe have got an overly used valve, I bought a new valve - installed - cleared codes - light came back on. I doubt the two issues of the EGR valve code and the engine stalling after start up are connected but just in case...
Would the main relay, as mentioned in several responses to others questions be responsible for the stalling as well?

The fix will not be too difficult. It's either the main relay or the Ignition Control Module (ICM) and/or coil. It really sounds like the main relay and ICM are the culprits. Because of the age and mileage on the car, I would replace all three. This should restore "like new" performance and reliability.

The main relay is located left of the steering column. Turning the ignition switch on and off will help you locate the main relay, by allowing you to hear and feel it "click." Main relays often have 7 wires going to them.

Here's how to replace the ICM:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-4.html#post265896

The ICM and coil are likely external on your Accord. Still, the link above will offer perspective on why these crucial and problematic components should be replaced. If you want, try replacing the main relay and see if that solves the problem. If it does not, replace the ICM and then the coil. I recommend replacing all of these items every 120,000 miles or 10 years, whichever comes first.

You can buy all of these parts at AutoZone and have the work done in an hour or less.

Go to the AutoZone.com website for your distributor and you'll clearly see the ICM. It mounts with two screws.