Intermittent P0455 Code

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Mazda Protege5
I'm getting and intermittent P0455 code on my 03 P5. It's happened 3 times in the past 6 months. When I clear the code, it goes away for a few months.

Any suggestions on what to look for? Since it happens so infrequently, I'm thinking a sensor issue versus something like a cracked hose or bad gas cap.
 
I'm thinking you've got a leak or block all the time but you only rarely meet all the conditions to pop the code.

 
Thanks for the info. Where are the purge solenoid valve and CDCV? I know there's a lot of stuff up in the left rear wheel well.
 
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