I'm back again with the same issue.

About 6 months ago i moved from Massachusetts to Park City, UT. I had some idling issues and logging the timing advance and saw it was outside of the +/-5 degrees the service manual calls for and still centered around the stock value. At the same time I got a check engine light for the ERG valve.

Every time the light has come on, it goes back off in a few days of driving to and from work. My daily commute must just be enough to get thought the required number of drive cycles, but not enough to cause the fault again.

I reset the computer and started the car without touching the gas and let it "learn" it was no where near sea level any more. Logging the timing now, it it seems to be in the factory specs now.

I still have my rough idle and when the car gets driven for a while (like 45 minutes or more) the idle gets worse and any my check engine lights comes on for the EGR valve. Again, after a few days of just daily commuting (about 10 minutes each way) the light goes out.

I checked all the vacuum lines and everything is attached and secure.

Any ideas?

Could a faulty O2 sensor cause this issue at idle, but not cause a fault to turn the check engine light on?

Thanks!

-matt