i've tried a couple of times but couldn't find any "large leak" spot. Couldn't hear anything different either. I did not crowl under the car, but was looking for leak from the top.

I noticed one thing: I used to hear the tapping sound from the purge valve, it was relatively loud, this time when I was looking for the leak, I could hear nothing.

If this one goes bad, would this cause the issue I have?

Thanks.

 

I finally had my Indy looked at it and he found out both the purge valve and the vent valve were not closing. I know where the purge valve is, can someone let me know what the vent valve is?