Anything in the evap system which could leak vapors should be checked.
This includes the purge control valve, canister, vapor piping, fuel tank
and filler neck.
It may be less expensive at this point to take the car to the dealer to be
checked. The dealer has the capability with their equipment to make the
evap leakage test run and check the system. By blocking off different
areas of the system and rerunning the test, the area of leakage can be
found by process of elimination.
The shop to which you're taking your car may also have a smoke machine.
This machine fills the system with smoke and the leak is found by
searching for the area where the smoke exits. I've had great difficulty
using this method-- I can almost never see the smoke.