Very odd problem, please help!
 

I took my car to the garage yesterday for a check-up. Basically just needed to check out the fuel pressure regulator and have the wideband recalibrated. All went well. When i got close to home, the dach lights came on (Just the battery light, tail light symbol, and hand brake symbol), the Air/Fuel went crazy lean, and the idle droped and ran kind of rough. The problem comes and goes, sometimes quickly and sometimes it stays for a bit. Any ideas? It's a brain buster! I think it might be the ground for the battery, or the alternator going bad, or a problem with an injector. The problem just happened out of nowhere, everything was fine, and then....

found it
 

I found the problem. I dont know how it happened but the nut on the alternator wire was loose. Just a quick tightening, and i was good to go.