Excessive fuel consumption in Honda Accord

Good evening all. Yesterday, a client told me to fix his excessive fuel consumption in a 2003 v6 Honda Accord. Engine was idling okay but about every 2-5 minutes at idle the engine idling would be so low as if it ones to go off but would regain power after that by itself. The low idling would be always about 5-10 second only. But after every about 4-6 spontaneous low idling  This scenario reoccurred as long as the engine was left idling. 
    In addition, the client took me on a test drive and complaint off gas, like pepper entering is eyes, I testified to that fact too.  
   These were the codes I retrieved below:
  drive.google.com/file/d/1lpmj3DlLVl71UYN...ny/view?usp=drivesdk

Please, what could be responsible for that?

find leak , injector seals and or evap line FIRST

Thank you so much for the guide! Sorry, I didn't complete what diagnosed!
I did replace the O2 sensor that's close to the firewall because after using a multimeter to conduct the test, I discovered that it was faulty.
As a result, I didn't notice the rough idle again and stalling stop then but I don't know if it reoccurred after I left. I cleared the codes and it all went away too except the P0498 that was the only one that remained. But don't know if others came back again.
Recently, the client called and said the car is still consuming fuel. Please, what should I do from here?

I think you'll have to get the car back in and see what codes did return and make sure the vent valve is working properly. If it hasn't been venting or properly purging, the cannister could be saturated.

Thank you sir. Please, are there ways to fix the issues?

Please, are there any test I should conduct? How can I verify that the purge valve or EVAP canister, are okay?

There are ways to fix the issues, once you get a look at the car again. You could disconnect the vent valve and replace it with a test light. If you have a bidirectional scan tool, see if the light turns on when you command on the valve, and is off when the vent is supposed to be off. See if you can blow through the vent valve when it's open.

That's all assuming no other codes are in there when you get it back.

Thank you so so much for sharing this great trick you've shared with me!
I don't have a bidirectional scanner for now. However, when would I know that it's the right time to blow air through? Please, how can I know that the valve it's open so I blow through it?

sir the best way i did is to look at utube vid s on these subjects . there you can see most of what we are talking about . good luck