[DoubleDingo]

yes, you should be able to blow air thru when open, no air when closed. The problem with the old valves is that "gunk" can get inside and coat the inside of the valve and it won't "fully" close. So after I changed my valve, I had a smaller leak from the other old valves in the emission system. I could tell it was getting better because the time between CEL was longer. So I tried cleaning my emission lines with Berryman B-12 (no difference) and then SEAFOAM. After the first bottle of SEAFOAM in the gas tank, the CEL didn't come back for 200 miles. When it came back, another bottle stretched the CEL to 600 miles. Third bottle and I am up to 1000+ miles. So far the SEAFOAM is working for me.

Hmmm...multiple applications of cleaner to the tank and it prolonged it each time... Mine spit out the P4220 small leak code and I already had a brand new Subaru Cap, so I cleaned the mating surface and gasket of the cap. Then added some Marvel Mystery Oil to the tank and had a small trip out of town, but the CEL flashed again when I was almost home, but this time the code was the P0456 very small leak. Each time my CEL triggers it is when I am driving on the open road. I can drive in town and it will never come on, but a few hours of highway driving and it triggers. I need to dig around like @Ski-Free is doing just to verify the status of things, but I am wondering if mine just needs some more cleaner ran through it like you did.

I have heard from Jackie that 2007's, and I am guessing it might include '06 thru '08, that the canister is an issue with these models. The vent valve is part of the canister too. I don't know it is just XT models or if it across the board. I didn't ask her that because mine is the on the problem-child-list when it comes to canisters.

Once in a while I can smell gas fumes, and other times I cannot. Like earlier this week, gas vapors were present when I was downwind of the car, now they're not. When I could smell them the tank was near 1/4, now it is full. I want to drive it on the open road to see if the CEL will come back but right now it is parked for the upcoming timing belt replacement. While it's down I need to also inspect the filler neck and canister area.

I will be following this thread to chime in on what I find and to see if you were able to fix yours. I have emissions testing in June 2019 and I need to make sure this issue is fixed for good.

 

[DoubleDingo]

The CEL only comes on after the ECU runs two EVAP systems test and they fail. For it to run them there are specific conditions that need to be met that are usually favourbale to highway driving so that’s why you’re seeing the CEL only come on when on the freeway..........

I did not know that, thanks you.

Mine had the intermittent gas smell also. Had to change the fuel tank vent valve to get rid of the smell on my forester, it's on top of the gas tank, was accessible from the back under the carpet.

I'll check that out when I do my searching around for leaks back there. My timing belt project got put on hold mid way through, so digging around for leaks got pushed back as well.

 

[DoubleDingo]

So check this out. We went on a 4,000+ mile drive over Christmas 2018 and New Years. Before we left I took some sil-glyde and smeared a thin film of it on the gasket of the gas cap. Guess what, no more evap codes! It requires the cap to be tightened really well, like three good turns, not revolutions, just three good turns that make the cap click. For those of you that can't seem to find the very small leak, it may just be the gas cap gasket needs some lube on it to allow a better seal at the filler neck. The only time the codes came back was when my wife filled it up while I was inside buying something. After that I made sure to turn a few more times and in a month's time, the p0442 and p0457 have stayed away. Prior to the sil-glyde even tightening the cap really well would result in the p0442 coming back. So give the sil-glyde a try if you still get the codes and nothing else appears to be wrong with the other components.