Volvo Repair: Car surging really bad, vacuum leak, air vacuum

Question
I have a s70 98 and it has been surging really bad. I have replaced the IAC and checked the hoses around it and it'll stop for minute then it will start back. It runs okay without the IAC being plugged up and then I'll plug it up again and it starts to surge. Plus my check engine light has come on and stays on. The obd2 tells me it's the evaporative leak but i can't find the cannister. can you give me some guidance on these two issues.

Answer
   Clyde, somewhere you have a large vacuum leak. Have the vehicle "smoke tested" to #1 find it and #2 to test the evap. system. I bet when you find the leak, it cures both problems.
  Here's what happens, unmetered air (vacuum leak) gets into the engine causing the idle to increase above 1500rpm. The powertrain logic sees closed throttle and too high idle and trys to compensate by closing the IAC, which then in turn almost kills the motor, seeing that, the IAC is snapped open and the cycle repeats.

Mark