altitude and the P0441 OBD

[drewd]

I have a 1999 Avalon with 80,000 miles. I have had the P0441 and P0446 obd codes and the CEL light on. I went up into the VA mountains ~ 3,000 ft and the CEL went out and stayed out for about 200 miles after I returned to sea level.
My question to the group - what is the relationship between altitude and the trouble codes? 0441 is low gas flow. I had seen that someone else had the same experience with codes clearing themself with altitude.

Second question - where is the VSV and the carbon canister located?

Thanks,
Drew Daniels