Weird problem with 1990 Corolla!

Hello everyone!
I really have enjoyed this site so far.
I bought a 1990 Corolla over the winter. The car did not run when I bought it because the fuel pump had failed. I installed a used "after market" fuel pump and the car ran great
Than summer rolled around and all that changed. The car runs fine when it is cool outside. Like on the way to work temps are running around 70-75 and there is no problem,but on the way home temps are pushing 90-95 and the car starts running bad like it is running out of gas.
The funny thing is you can turn the ignition switch off and back on while driving and it will stop missing for a minute or so. Also when it is hot and running bad I can put gas in it and it will not miss at all. I wonder if it is because the gas is cooler straight from the pump vs. sitting in the car all day? Anyways I am sorry this is such a long thread but any help would be appreciated.

P.S. I have changed the fuel filter and also I can tank the cap off the gas tank and hear the fuel pump running at what seems like different speeds(it revs up and down) when the car is missing

have you checked the fuel pump relay? maybe that is what is going bad.

Did you ever work out the problem, i have a corolla wagon and it is doing pretty much the same thing.

i have a thread about this too...hoping to get an answer that fixes it for me...

must be a common problem after all..

i am in louisiana where morning is 70 and afternoon is like 95 too and exact same prob