P0455 & P0171 Codes

My idle got really rough, but my vaccum has been stable and great. However today they following two codes got thrown and I need help tracking it down. Its a vacuum leak cause when I am at a stop ight everything is fine, idling good and then I see the vacuum go down and the idle goes to crap. Never stalls but runs rough. So the P0455 is the hint. Which is the "Gas cap code" or EVAP Emissions Control System Leak. Anyone see this before? I need to go check all the vaccuum lines to the purge valve, etc

i say check your intercooler cooler hose going up from the compressor cuz mine does the same thing cuz the hose is cracked