We have an Audi A8 2005 4.2 and we live in Arizona. We drive 2X/yr to Paso Robles California to pick up some nice wine. Each time, when we arrive in Paso Robles, and drive around, we get a check engine light, which disappears when we leave. We don’t get this in other states or even other parts of California.
Do you live in the high desert of Arizona? The gasoline is usually lower in octane (85-86 octane) than gas at sea level. I used to live in Sierra Vista and my Cherokee use to run a little differently on California gas until the engine acclimated. This may be what’s happening to you. Have you had the codes read when this happens?
Even though the light went out (lucky you) the computer should have stored the code that caused the light. Most parts stores will read the codes for you free. At least you will know why the light came on…