I have a 1998 Lexus ES 300 with 217,000 miles. I have a PO446 code for vent valve. I replaced the charcoal canister about 2 1/2 years ago and a new vent valve was on that canister. I bought an aftermarket vent valve and replaced it but the same code came back. I've erased it 3 times and I've noticed that every time the check engine light came back on, I was at a stop light in idle. I checked all the hoses and everything looks good and nothing out of place. I've also replaced the gas cap with an OEM in the last couple years. What do you think it could be??
As Scotty says, start simple and cheap. If you haven't done so, check the fuel tank filler neck (that feeds into the gas tank, when you fill up). It's plastic, and plastic cracks and bends over time. (I've had to change a number of plastic parts on my 2008 Camry).
Also, have all the electrical connections (including the newer vent valve) checked for proper power/ground, if you haven't yet done so.
Finally, if you can get hold a factory manual (it might be the same as the factory manual for a Camry of that year, BTW), you could go through the troubleshooting issues, one-by-one.
