car is a 1990 Civic EX. When the weather is cool, as in anywhere below about 65 F, the car starts right up with no problem whatsoever. As soon as the weather gets warmer (and in San Diego it gets warm rather early), the car won't start. It will crank over, it has spark, and it has fuel. It's something apparently caused by heating that isn't allowing the car to start. Please advise.

 

i had a prelude that did the same thing. i was told to replace the TW sensor even though i was not getting a code for it. it took care of the problem.

 

what does TW stand for?

I should mention, since you bring it up, that this car also isn't throwing any codes. It's really strange. Maybe this "TW" sensor will be the problem.

 

Coolant temperature sensor.

I'd put my money on the main relay though.

 

My money's on the main relay too. I had the same problem in my crx, and after replacing the relay, haven't had the same problem anymore. It should be right behind the driver's side kicker panel. You can do a search on here and find a thread I started on it, plus I posted a pic of it.

 

Main relay. I have replaced over a million of them fixes problem everytime.

 

i say main relay because i just had to change mine about a month ago when the weather started to get hot.