Whenever I take the evo out for a drive on a very hot day the idle feels like it will stall but it never stalled. Feels like and sounds like its misfiring but only at idle. When driving through city or highway I don't have any issues except the idle part. On a warm/cool day I don't have any issues at all.

What seems to be the problem?

parts:
injen intake with perrin air filter
intercooler pipes
evo 9 diverter valve
hallman mbc
jmf o2 dump
maperformance crank case kit
milspec tb seals
br exhaust with highflow cat and magnaflow muffler
and a very old tune from 2005

 

Sounds like the tune could be it, a touch-up tune should do the trick

 

are you running your a/c? Could be the compressor motor kicking in and out. If you have a partially plugged expansion valve, your compressor could be putting a high load on the motor, and as it kicks in and out (on high discharge pressure), it will jack with the idle. Ask me how I know......