Toyota Repair: Camry bucks and intermittently loses power in warmer weather, toyota camry, emission system


Question
2001 Toyota Camry CE 6 cylinder 120,000 miles on it.  Found out after I bought it in 2003 that it had been wrecked. I love this car BUT - I have the following problem (multiple mechanics including Toyota have not been able to figure out):

*Occurs only in warmer weather.
*Does not occur in colder weather at all, even on long trips or when engine warms up
*What happens - between 1 and 2000 RPM, the car "bucks" and the RPMs fluctuate.  Occasionally also I will hit the brake to slow down and the engine just stops completely with no sound or warning, again usually when going 1-2k rpm
*It seems worse for a while after I get gas.
*It is intermittent - there is no predicting when it might or might not occur.
*Sometimes it goes on repeatedly for days, other times just once in a while.
*Should also note my check engine light comes on frequently and mechanic said it has to do with my gas tank/emission system - not sure about the details of that. He said just make VERY sure I screw the gas cap on tightly.

Thank you for your help!

Answer
The first thing I'd need to know is to see what codes are stored in the computer, after the check engine light comes on again have the trouble codes read and write them down and let me know what they are, I need the code numbers only, not the mechanics explantion of what it might be.