I have an 03' chevy silverado 1500 with only 95,000 miles. It's having a rough idle. It lopes at idle but as soon. As you give it gas it idles fine for a few seconds and then goes back to loping. It runs completely fine while driving down the road. The codes are saying bank 1&2 are running lean and misfires. We can't seem to think of the problem of what is going on. Any ideas?

SOURCE: 2001 Forester, Rough idle and engine loping driving at low rpm

I had a similar problem on my 2002 Impreza RS 2.5 (same engine and engine control system). In my case it was the O2 sensor on the intake manifold. This happened at 34,xxx mi. so it was covered by the warranty. Replacing the part is very easy. (two bolts and a wiring harness). Obviously I would start simple and cheap and work your way to expensive and difficult.
From my understanding its all caused from the engine missfiring. If its been a while or never, I'd change the spark plugs first. (stick with the Subaru Parts plugs, I went after market and the dealer claimed the plugs were not the correct "temperature" and had to pay for the new plugs and install although they did it without my permition. Thats a whole nother story).
Could also be the manifold pressure sensor.
Either 02 or manifold pressure sensor may cause intermitent check engine light.
Where I live Brookline,MA , Autozone will run a free diagnostic on your car by hooking up to your ECU and will give you the trouble codes and possible remidies. Of course there are no guarentee's but it will point you in the right direction.
Good Luck